Here's a diverging diamond interchange where traffic seems to be needlessly backing up through the adjacent intersection. Would a SPUI or even roundabouts be more effective than existing diverging diamonds? I don't see many advantages that diverging diamond interchanges have over other designs.
(https://www.aaroads.com/forum/proxy.php?request=http%3A%2F%2Fi478.photobucket.com%2Falbums%2Frr144%2Ftradephoric%2FTransportation%2520Pictures%2FRandom%2Fdivergingdiamond_zpsvbfqs1sf.png&hash=ef3f75d4854dec58f35bc2d1523ef955f6845a8d) (http://s478.photobucket.com/user/tradephoric/media/Transportation%20Pictures/Random/divergingdiamond_zpsvbfqs1sf.png.html)
https://maps.google.com/maps?ll=37.25132,-93.31049&z=17&t=h&output=classic&dg=brw
IMHO, DDI's are most effective if the majority of the surface road traffic changes direction onto or off of the freeway. If the majority of surface road traffic is only thru traffic and does not turn onto the freeway, then the DDI is not the best solution as the thru traffic may commonly have longer waits to clear the interchange vs. a traditional diamond interchange. At that point, I would opt for a SPUI.
A DDI has two and only light phases. A SPUI needs at least three, and I've seen the local one have as many as six at times, seemingly at random. Wouldn't that make it take longer to get through a SPUI?
SPUIs require expensive new bridgework. A standard diamond can be converted into a DDI with no changes to the existing bridge, just some concrete work on either side of it. Major capacity boost for a small fraction of what any other solution would cost. Very useful in a state like Missouri that has some of the worst highway funding problems in the nation.
Maybe it's my lack of a background in civil engineering, but I fail to see how the problem with stacked thru traffic at the demonstrated intersection would be improved using a SPUI or normal diamond.
Quote from: Thing 342 on March 25, 2015, 08:32:14 PM
Maybe it's my lack of a background in civil engineering, but I fail to see how the problem with stacked thru traffic at the demonstrated intersection would be improved using a SPUI or normal diamond.
In most interchange designs, thru traffic on the surface road can proceed simultaneously in both directions. But the DDI prioritizes turning traffic over thru traffic, meaning that only half the total time can be assigned to each direction.
DDIs are also easier for larger trucks (read: OSOW) to navigate. There have been a couple DDIs selected over roundabouts in Wisconsin with OSOW accommodations being one of the biggest reasons.
Here's a roundabout interchange outside of Milwaukee on I-43. This appears to have similar if not less ROW requirements than the DDI example from Missouri. Overall, would two roundabouts be cheaper than a DDI (since there are no traffic signals to maintain, same ROW requirements)?
https://www.google.com/maps/@42.9327037,-88.160052,577m/data=!3m1!1e3
What about doing something like this interchange in Texas? Thru traffic on the street tunnels under the access roads so the only traffic at the lights are the access road and turning traffic from the street.
https://www.google.com/maps/place/Richardson,+TX/@32.940039,-96.745678,346m/data=!3m1!1e3!4m2!3m1!1s0x864c1ee979bea767:0x2cdb29c046270495
Quote from: dfwtbear on March 25, 2015, 11:04:30 PM
What about doing something like this interchange in Texas? Thru traffic on the street tunnels under the access roads so the only traffic at the lights are the access road and turning traffic from the street.
https://www.google.com/maps/place/Richardson,+TX/@32.940039,-96.745678,346m/data=!3m1!1e3!4m2!3m1!1s0x864c1ee979bea767:0x2cdb29c046270495
Interesting. I had assumed that this similar interchange in Royal Oak, Michigan was unique:
https://www.google.com/maps/place/Royal+Oak,+MI/@42.4744205,-83.1454238,587m/data=!3m1!1e3!4m2!3m1!1s0x8824c5f96ccd2bf7:0x70fd341efca3310 (https://www.google.com/maps/place/Royal+Oak,+MI/@42.4744205,-83.1454238,587m/data=!3m1!1e3!4m2!3m1!1s0x8824c5f96ccd2bf7:0x70fd341efca3310)
The above link just searches for the town of Richardson for me.
Quote from: dfwtbear on March 25, 2015, 11:04:30 PM
What about doing something like this interchange in Texas? Thru traffic on the street tunnels under the access roads so the only traffic at the lights are the access road and turning traffic from the street.
https://www.google.com/maps/place/Richardson,+TX/@32.940039,-96.745678,346m/data=!3m1!1e3!4m2!3m1!1s0x864c1ee979bea767:0x2cdb29c046270495
The Texas U-turn there. Helps traffic at intersections with one-way access roads as traffic wanting to turn around avoid 2 sets of traffic signals. Without knowing traffic patterns there it may be the optimal solution to a busy intersection with access roads.
Quote from: mhh on March 25, 2015, 11:31:57 PM
Quote from: dfwtbear on March 25, 2015, 11:04:30 PM
What about doing something like this interchange in Texas? Thru traffic on the street tunnels under the access roads so the only traffic at the lights are the access road and turning traffic from the street.
https://www.google.com/maps/place/Richardson,+TX/@32.940039,-96.745678,346m/data=!3m1!1e3!4m2!3m1!1s0x864c1ee979bea767:0x2cdb29c046270495
Interesting. I had assumed that this similar interchange in Royal Oak, Michigan was unique:
https://www.google.com/maps/place/Royal+Oak,+MI/@42.4744205,-83.1454238,587m/data=!3m1!1e3!4m2!3m1!1s0x8824c5f96ccd2bf7:0x70fd341efca3310 (https://www.google.com/maps/place/Royal+Oak,+MI/@42.4744205,-83.1454238,587m/data=!3m1!1e3!4m2!3m1!1s0x8824c5f96ccd2bf7:0x70fd341efca3310)
Those are technically volleyballs. Sure, they help thru traffic flow on the cross street, but they're probably significantly more expensive to build than a DDI, a roundabout interchange, or a SPUI, since you're looking at a three-level interchange rather than a two-level interchange.
IIRC, throughput on roundabouts is much lower than on a DDI. That Wisconsin example isn't really a similar situation, since that's basically a 2 lane rural road that happens to widen to 4 lanes for a mile surrounding the freeway, and travels through empty land and low-density residential areas, while the Missouri one has multiple large retailers plus the fairgrounds nearby, not to mention being the primary route between Springfield and the KC metro. Suggesting what was done at the US 75/Spring Valley interchange in Richardson is just silly, tunneling under an existing road without completely shutting it down and doing a cut and cover costs a fortune.
Looking through aerials on Google Earth of roughly 150 multi-lane interchange roundabouts and 30 DDI's, none of the interchange roundabouts seem to be experiencing any significant backups while several of the DDI's have significant backups on at least one leg (and in some cases are backing up through the adjacent intersection). Here's example of a higher capacity interchange roundabout that is also on I-43 (it's a 3-lane roundabout). Again, no significant backups.
https://maps.google.com/maps?ll=42.951318,-88.108882&spn=0.006471,0.006813&t=h&z=17
DDI's are simple two-phase traffic signals but the surrounding signals of a DDI are often complicated 4-phase signals which requires longer cycle lengths. Oftentimes, a DDI doesn't coordinate with a signal that might only be 600 feet away (such as the original example posted). When you have green to red coordination, you will inevitably see a queue of cars (that just got a green light at the signal 600 feet away) backing up along the DDI.
(https://www.aaroads.com/forum/proxy.php?request=http%3A%2F%2Fi478.photobucket.com%2Falbums%2Frr144%2Ftradephoric%2FTransportation%2520Pictures%2FRandom%2FDDIuntitled_zpspddozbup.png&hash=d45d931d1c1b7cae8ea0a07b8bb2da64f426f445) (http://s478.photobucket.com/user/tradephoric/media/Transportation%20Pictures/Random/DDIuntitled_zpspddozbup.png.html)
(https://www.aaroads.com/forum/proxy.php?request=http%3A%2F%2Fi478.photobucket.com%2Falbums%2Frr144%2Ftradephoric%2FTransportation%2520Pictures%2FRandom%2FDDI-rounduntitled_zpskm9dsbr9.png&hash=8f432d59953758f219a9dbb9dee839bb5d01f8a6) (http://s478.photobucket.com/user/tradephoric/media/Transportation%20Pictures/Random/DDI-rounduntitled_zpskm9dsbr9.png.html)
Quote from: tradephoric on March 26, 2015, 08:08:53 AM
Looking through aerials on Google Earth of roughly 150 multi-lane interchange roundabouts and 30 DDI's, none of the interchange roundabouts seem to be experiencing any significant backups while several of the DDI's have significant backups on at least one leg (and in some cases are backing up through the adjacent intersection). Here's example of a higher capacity interchange roundabout that is also on I-43 (it's a 3-lane roundabout). Again, no significant backups.
https://maps.google.com/maps?ll=42.951318,-88.108882&spn=0.006471,0.006813&t=h&z=17
DDI's are simple two-phase traffic signals but the surrounding signals of a DDI are often complicated 4-phase signals which requires longer cycle lengths. Oftentimes, a DDI doesn't coordinate with a signal that might only be 600 feet away (such as the original example posted). When you have green to red coordination, you will inevitably see a queue of cars (that just got a green light at the signal 600 feet away) backing up along the DDI.
Yes, DDIs are a pain to coordinate as part of a signalized corridor. While the roundabout you linked doesn't
usually have any significant backups, it has had a higher than normal crash problem. That pair of roundabouts have been a thorn in the side of the WisDOT SE Region since they opened. Those two gave the anti-roundabout crowd a lot of fuel and are part of the reason why WisDOT has put a moratorium on any more three-lane roundabouts in Wisconsin.
Quote from: DaBigE on March 26, 2015, 08:53:45 AM
Quote from: tradephoric on March 26, 2015, 08:08:53 AM
Looking through aerials on Google Earth of roughly 150 multi-lane interchange roundabouts and 30 DDI's, none of the interchange roundabouts seem to be experiencing any significant backups while several of the DDI's have significant backups on at least one leg (and in some cases are backing up through the adjacent intersection). Here's example of a higher capacity interchange roundabout that is also on I-43 (it's a 3-lane roundabout). Again, no significant backups.
https://maps.google.com/maps?ll=42.951318,-88.108882&spn=0.006471,0.006813&t=h&z=17
DDI's are simple two-phase traffic signals but the surrounding signals of a DDI are often complicated 4-phase signals which requires longer cycle lengths. Oftentimes, a DDI doesn't coordinate with a signal that might only be 600 feet away (such as the original example posted). When you have green to red coordination, you will inevitably see a queue of cars (that just got a green light at the signal 600 feet away) backing up along the DDI.
Yes, DDIs are a pain to coordinate as part of a signalized corridor. While the roundabout you linked doesn't usually have any significant backups, it has had a higher than normal crash problem. That pair of roundabouts have been a thorn in the side of the WisDOT SE Region since they opened. Those two gave the anti-roundabout crowd a lot of fuel and are part of the reason why WisDOT has put a moratorium on any more three-lane roundabouts in Wisconsin.
Good info DaBigE. That's the first i've heard about that moratorium. A 3-lane roundabout in SE Michigan was recently restriped as a 2-lane roundabouts. Of course, the roundabout was originally designed with the idea that the street it services would be widened to a 4-lane boulevard, but the street is still only a two-lane road. Therefore, the reduction in lanes hasn't had an adverse effect on throughput.
I need to get on a soap box for just a minute... I think the name "DDI" has already caught on and it's too late to convince people to call it something else, but "double crossover diamond" makes so much more sense. What about this interchange diverges more than other service interchanges? There are actually fewer diverging conflicts in a DCD than a normal diamond... I vote we all start going with "DCD" :-D
Anyway, good discussion here. I don't think they'll go away like a fad; the ability to minimize bridge area is crucial. I think they will be built in some areas that they shouldn't be (maybe this is a result of it being a fad?). Maybe the biggest DCD shortfall will be the frontage road coordination that someone else already touched on. On corridors with a lot of through traffic, problems at interchanges will get moved a few hundred feet to the next intersection and construction projects will be considered failures.
I'd like to see more of the aerial images, especially ones with queuing! In fairness, I don't think that one aerial image is indicative of the performance of an interchange. Plenty of things could cause this, maybe there was a crash nearby, it was the day of some special event, or the engineer was testing a new signal timing plan.
As far as roundabouts, one big problem is keeping them from totally failing on a busy corridor. Keep in mind they're typically designed for 20 years in the future so they should be fine after construction until lots of growth occurs. However, once they hit capacity they can fail (and queue) quickly. There is no control on arrivals if there are no signals metering the traffic; that's one reason signalized options like DCD are sometimes preferable.
Can anyone speak to how a DDI will handle traffic in a busy shopping area with multiple traffic signals? PennDOT is converting the US 19 at I-70/79 in Washington, PA. US 19 already has 5 signals in a little over a mile stretch (one south of the interchange, four north) through an area with four separate shopping areas.
I travel this area almost daily and I recognize that the US 19/I-70/I-79 interchange is in drastic need of updating. I am no way suggesting that a DDI is wrong here - I don't have anywhere near the training or education to make that decision. But, as a driver in this area, I worry about an often congested corridor becoming even worse.
^ Since the I-70/I-79 interchange is a full cloverleaf, I would question whether a DDI would work better than removing two of the loops. I would assume since the shopping area north of I-70/I-79 appears to be on the edge of town there would be a decent amount of through traffic. Therefore it might not be the best place for a DDI, but the five-way intersection to the south may do a good job of metering traffic into the interchange.
Quote from: Revive 755 on March 26, 2015, 05:12:38 PM
^ Since the I-70/I-79 interchange is a full cloverleaf, I would question whether a DDI would work better than removing two of the loops. I would assume since the shopping area north of I-70/I-79 appears to be on the edge of town there would be a decent amount of through traffic. Therefore it might not be the best place for a DDI, but the five-way intersection to the south may do a good job of metering traffic into the interchange.
Thanks for the input. PennDOT has plans to remove all four loops of the cloverleaf and just keep the four outer ramps. There is some information here on the overall project: http://www.i-70projects.com/I-70andI-79NorthJunction.html
As for the shopping areas, my experience tells me that stretch of US 19 (between I-70/I-79 and Cameron Rd.) has a decent amount of traffic from ~8 a.m. until ~9 p.m., with obvious fluctuations at lunch time and in the evenings. Saturday afternoon can also be tricky.
Quote from: Revive 755 on March 26, 2015, 05:12:38 PM
Since the I-70/I-79 interchange is a full cloverleaf, I would question whether a DDI would work better than removing two of the loops.
I think one of the reasons of the DDI over that idea is so they can use the existing bridges over US-19 while 6-laning I-70/79. If they left some loop ramps in, They'd have to use what will be the outer I-70/79 lanes as acceleration/deceleration (depending on what loops were left) lanes for the ramps instead.
Have the safety numbers on that interchange in New Berlin been improving lately? If so, I'd chalk that up to what I call the 'drivers ed' issue - getting people up to speed on how they work and how to use them.
The roundabouts around here, including a few with three lanes, appear to me to be working well with good safety.
Mike
It's true: DDIs take almost no new driving skills to master if you've never encountered one before. Normal merges and straight-through stoplight movements. Roundabouts, however, take a couple of new ways of thinking for drivers unfamiliar with them: everyone keeps moving rather than everyone stopping, priority goes to the left, occasional exits from an inner lane, etc.
In a perfect world, no one stops at a roundabout, but I've been in plenty of scenarios where they were so clogged that it was necessary to stop for a minute or two before entering. I'm thinking of Happy Valley Rd and I-17 in Phoenix, in particular.
The DDI concept really seems to be taking hold in Utah, where I saw several completed and some under construction a few weeks ago. I ate lunch at a restaurant in American Fork where the intersection was plainly visible from my table. I watched, and never saw any traffic stack up. As another poster mentioned, the through movement gets shafted a little in the DDI. The signal was set up so the Eastbound thru movement from the bridge had a green at the same time as the northbound ramp onto the bridge. I assume the same setup was in place for Westbound from bridge and Southbound from Ramp. It was definitely interesting to watch; I even saw a funeral procession go through without a hitch, albeit with several escorting officers.
Quote from: BigRedDog on March 26, 2015, 04:25:00 PM
Can anyone speak to how a DDI will handle traffic in a busy shopping area with multiple traffic signals? PennDOT is converting the US 19 at I-70/79 in Washington, PA. US 19 already has 5 signals in a little over a mile stretch (one south of the interchange, four north) through an area with four separate shopping areas.
I travel this area almost daily and I recognize that the US 19/I-70/I-79 interchange is in drastic need of updating. I am no way suggesting that a DDI is wrong here - I don't have anywhere near the training or education to make that decision. But, as a driver in this area, I worry about an often congested corridor becoming even worse.
There is one I went by where the left turn phase of the shopping center had a very extended green tied to the green in the same direction right after the DDI.
I drove through all of Utah's DDI's multiple times for work and they functioned beautifully in my experience. I can't wait to see them in Wisconsin.
I think of how much extra money was put into the interchange at I-43/894 and 27th Street to put in those low-speed semi-directional ramps to handle 'left' turning traffic onto the freeway. A DDI would've been a much, much cheaper and equally effective option. Could've used the money saved to rebuild the Howard Ave overpass to accommodate a SB auxiliary lane between the Holt Ave entrance and the Howard Ave exit.
Talk about a 'fad'; those types of ramps in the Milwaukee area are going to be one. In addition to that example, WisDOT put them in at I-41 and Watertown Plank and another at I-94 and WI 100. Watertown Plank; there's another one where a DDI would've been way, way, way cheaper and handled the traffic just fine.
Quote from: Mr_Northside on March 27, 2015, 01:47:45 PM
Quote from: Revive 755 on March 26, 2015, 05:12:38 PM
Since the I-70/I-79 interchange is a full cloverleaf, I would question whether a DDI would work better than removing two of the loops.
I think one of the reasons of the DDI over that idea is so they can use the existing bridges over US-19 while 6-laning I-70/79. If they left some loop ramps in, They'd have to use what will be the outer I-70/79 lanes as acceleration/deceleration (depending on what loops were left) lanes for the ramps instead.
I see your point here. They are saving money by not having to widen I-70/79 bridge to accommodate acceleration/deceleration lanes. I'm just ultra sensitive to designs that screws with coordination along a main arterial. It's commonplace to drive 10+ miles without getting stopped at a red light along major arterials in Metro Detroit. If DDI's start taking off here, the game of seeing how far you can go without getting stuck at a red light won't be as fun. The smooth coordination seen along Big Beaver Road in this video would be impossible if a DDI replaced the full cloverleaf interchange at I-75:
https://www.youtube.com/watch?v=eB2H4bGp4Jc
Quote from: triplemultiplex on March 29, 2015, 09:47:30 AM
I can't wait to see them in Wisconsin.
One is being planned for the WI 441 / US 10 / Oneida St interchange by Menasha.
Quote from: Big John on March 29, 2015, 10:50:26 AM
Quote from: triplemultiplex on March 29, 2015, 09:47:30 AM
I can't wait to see them in Wisconsin.
One is being planned for the WI 441 / US 10 / Oneida St interchange by Menasha.
It's actually in Appleton (you just gotta love Wisconsin's failed municipal boundary law! :spin: ).
Also, WisDOT has *firm* plans for DDIs at I-39/90/WI 26 in Janesville and I-39/90/WI 81 (Milwaukee Rd), piggybacked on the I-39/90/I-43 ('Beloit' interchange), in Beloit.
Mike
Quote from: triplemultiplex on March 29, 2015, 09:47:30 AM
I think of how much extra money was put into the interchange at I-43/894 and 27th Street to put in those low-speed semi-directional ramps to handle 'left' turning traffic onto the freeway. A DDI would've been a much, much cheaper and equally effective option.
That interchange looks like something designed during the Reagan administration.
From an engineering perspective, DDIs are superior to SPUIs in almost every case. While roundabouts are better in theory, people don't know how to use them. As previously stated, you only have to put down a little bit of concrete and change the striping and signals to get a major improvement, as both signals in the intersection are coordinated. Are they great when there are many adjacent intersections? No. But they are often many times better than the diamonds they replace. They're probably best in medium-traffic situations or when having each direction on different phases doesn't matter.
SPUIs and roundabouts have a bit of a learning curve. DDIs have less of one.
Quote from: mgk920 on March 27, 2015, 10:48:26 PM
Have the safety numbers on that interchange in New Berlin been improving lately? If so, I'd chalk that up to what I call the 'drivers ed' issue - getting people up to speed on how they work and how to use them.
The roundabouts around here, including a few with three lanes, appear to me to be working well with good safety.
Mike
I haven't seen the official latest crash numbers, but I've been told Moorland Rd is getting better. The roundabout haters still make a comment every now and again, but their minds are made up.
And for the record, one more 3-laner squeaked approval, mainly because things were too far down the road to change (funding, design, etc.): Wis 47 and CTH OO (Richmond St at Northland Ave) in Appleton.
Quote from: mgk920 on March 29, 2015, 11:32:45 AM
Quote from: Big John on March 29, 2015, 10:50:26 AM
Quote from: triplemultiplex on March 29, 2015, 09:47:30 AM
I can't wait to see them in Wisconsin.
One is being planned for the WI 441 / US 10 / Oneida St interchange by Menasha.
It's actually in Appleton (you just gotta love Wisconsin's failed municipal boundary law! :spin: ).
Also, WisDOT has *firm* plans for DDIs at I-39/90/WI 26 in Janesville and I-39/90/WI 81 (Milwaukee Rd), piggybacked on the I-39/90/I-43 ('Beloit' interchange), in Beloit.
Mike
IIRC, there is at least one on the drawing board for the I-43 corridor between Grafton and Milwaukee.
Quote from: DaBigE on March 30, 2015, 01:42:26 PM
Quote from: mgk920 on March 27, 2015, 10:48:26 PM
Have the safety numbers on that interchange in New Berlin been improving lately? If so, I'd chalk that up to what I call the 'drivers ed' issue - getting people up to speed on how they work and how to use them.
The roundabouts around here, including a few with three lanes, appear to me to be working well with good safety.
Mike
I haven't seen the official latest crash numbers, but I've been told Moorland Rd is getting better. The roundabout haters still make a comment every now and again, but their minds are made up.
The chart below looks at crash data of 16 major roundabouts built throughout SE Michigan between 2006-2009. While PDO accidents spike the first year after roundabout construction, injury accidents drop from day one. By year two people seem to get use to them and the PDO steadily declines from the initial spike. This has at least been the trend for SE Michigan.
(https://www.aaroads.com/forum/proxy.php?request=http%3A%2F%2Fi478.photobucket.com%2Falbums%2Frr144%2Ftradephoric%2FTransportation%2520Pictures%2FRoundabouts%2FRBuntitled_zps758a2437.png&hash=72057a190f81fe343b369787fc1cee4936efece8)
Quote from: DaBigE on March 30, 2015, 01:42:26 PM
Quote from: mgk920 on March 27, 2015, 10:48:26 PM
Have the safety numbers on that interchange in New Berlin been improving lately? If so, I'd chalk that up to what I call the 'drivers ed' issue - getting people up to speed on how they work and how to use them.
The roundabouts around here, including a few with three lanes, appear to me to be working well with good safety.
Mike
I haven't seen the official latest crash numbers, but I've been told Moorland Rd is getting better. The roundabout haters still make a comment every now and again, but their minds are made up.
And for the record, one more 3-laner squeaked approval, mainly because things were too far down the road to change (funding, design, etc.): Wis 47 and CTH OO (Richmond St at Northland Ave) in Appleton.
I am well familiar with that intersection, it is the most dangerous in the entire City of Appleton. All of the needed ROW is there for it, too - when Northland Ave (Outagamie County 'OO') was originally built as US 41 in the late 1930s, the Wisconsin Highway Commission (predecessor of WisDOT) acquired enough additional land to allow for generous 'vision corners' at the major intersections along that then new two-lane rural bypass highway.
Mike
Quote from: mgk920 on March 31, 2015, 01:04:21 PM
Quote from: DaBigE on March 30, 2015, 01:42:26 PM
Quote from: mgk920 on March 27, 2015, 10:48:26 PM
Have the safety numbers on that interchange in New Berlin been improving lately? If so, I'd chalk that up to what I call the 'drivers ed' issue - getting people up to speed on how they work and how to use them.
The roundabouts around here, including a few with three lanes, appear to me to be working well with good safety.
Mike
I haven't seen the official latest crash numbers, but I've been told Moorland Rd is getting better. The roundabout haters still make a comment every now and again, but their minds are made up.
And for the record, one more 3-laner squeaked approval, mainly because things were too far down the road to change (funding, design, etc.): Wis 47 and CTH OO (Richmond St at Northland Ave) in Appleton.
I am well familiar with that intersection, it is the most dangerous in the entire City of Appleton. All of the needed ROW is there for it, too - when Northland Ave (Outagamie County 'OO') was originally built as US 41 in the late 1930s, the Wisconsin Highway Commission (predecessor of WisDOT) acquired enough additional land to allow for generous 'vision corners' at the major intersections along that then new two-lane rural bypass highway.
Mike
I'm actually working on that intersection project right now. The fixes needed to make the signals an operationally-acceptable solution were ugly from just about every perspective.
Quote from: DaBigE on March 30, 2015, 01:42:26 PM
Quote from: mgk920 on March 27, 2015, 10:48:26 PM
Have the safety numbers on that interchange in New Berlin been improving lately? If so, I'd chalk that up to what I call the 'drivers ed' issue - getting people up to speed on how they work and how to use them.
Mike
I haven't seen the official latest crash numbers, but I've been told Moorland Rd is getting better. The roundabout haters still make a comment every now and again, but their minds are made up.
The Moorland Road roundabout has a central island diameter of nearly 190 feet. This is a BIG roundabout that is approaching traffic circle dimensions. There are other 3-lane interchange roundabouts with central island diameters that are much smaller. For instance, the central island of the 3-lane interchange roundabout at Sawyer Road and I-94 is only 100 feet.
Utah is using them on their highest volume service interchanges which suggests they are best at moving traffic in tight spaces where loop ramps are out of the question. I saw one under construction in Brigham City where US 91 ends at I-15 and even though there is one dominant "left turn" movement through that interchange, the DDI was still a better option, apparently, than putting in loop ramp.
This ain't going to be no fad. Nationwide, DOT's are going to save billions over the next two decades building DDI's instead of all other types of high-volume service interchanges that require more land or more expensive bridges. It should become the default design used in metropolitan areas, in my opinion.
Quote from: triplemultiplex on April 01, 2015, 10:54:21 PM
Utah is using them on their highest volume service interchanges which suggests they are best at moving traffic in tight spaces where loop ramps are out of the question. I saw one under construction in Brigham City where US 91 ends at I-15 and even though there is one dominant "left turn" movement through that interchange, the DDI was still a better option, apparently, than putting in loop ramp.
They are. 2011 Green Book requires very large curve radii for a decent design speed. Ontario's many parclos often have recommended speeds of 30 km/h (about 20 mph) on the loops because larger loop ramps are cost-prohibitive.
Quote from: Big John on March 25, 2015, 11:51:09 PM
Quote from: dfwtbear on March 25, 2015, 11:04:30 PM
What about doing something like this interchange in Texas? Thru traffic on the street tunnels under the access roads so the only traffic at the lights are the access road and turning traffic from the street.
https://www.google.com/maps/place/Richardson,+TX/@32.940039,-96.745678,346m/data=!3m1!1e3!4m2!3m1!1s0x864c1ee979bea767:0x2cdb29c046270495
The Texas U-turn there. Helps traffic at intersections with one-way access roads as traffic wanting to turn around avoid 2 sets of traffic signals. Without knowing traffic patterns there it may be the optimal solution to a busy intersection with access roads.
The Texas-style U turn ramp is brilliant. Whoever designed it should be canonized. I live near one of these and it's nice to be able to go in the opposite direction on the frontage roads without having to make 2 left turns and without having to wait for the signals to cycle. Any highway with frontage roads should use these highly useful ramps whenever possible.
As for the Death Diamond, the designer should be drawn and quartered. Terrible, terrible design. The only reason there haven't been more fatalities are because the travel speed is very slow.
Quote from: johndoe on March 26, 2015, 03:40:43 PM
I need to get on a soap box for just a minute... I think the name "DDI" has already caught on and it's too late to convince people to call it something else, but "double crossover diamond" makes so much more sense. What about this interchange diverges more than other service interchanges? There are actually fewer diverging conflicts in a DCD than a normal diamond... I vote we all start going with "DCD" :-D
The term "Death Diamond", coined by yours truly, has caught on in the road community.
Quote from: bugo on April 02, 2015, 02:06:14 AM
The Texas-style U turn ramp is brilliant. Whoever designed it should be canonized. I live near one of these and it's nice to be able to go in the opposite direction on the frontage roads without having to make 2 left turns and without having to wait for the signals to cycle. Any highway with frontage roads should use these highly useful ramps whenever possible.
ODOT "experimented" with the Texas U-Turn when it built the Lakeland Freeway stretch of I-90/SR-2 in the mid 60s. (https://goo.gl/maps/DZ6MG), but it was never used elsewhere in Cleveland (mainly because there were very few frontage roads associated with the newer freeways being built).
I can think of a few interchanges in NEOH that should be retro-fitted with some sort of Texas U-Turn: This fustercluck in particular (between Alexander and Broadway): https://goo.gl/maps/3ohXd
Quote from: cl94 on March 30, 2015, 01:29:56 PM
From an engineering perspective, DDIs are superior to SPUIs in almost every case. While roundabouts are better in theory, people don't know how to use them. As previously stated, you only have to put down a little bit of concrete and change the striping and signals to get a major improvement, as both signals in the intersection are coordinated. Are they great when there are many adjacent intersections? No. But they are often many times better than the diamonds they replace. They're probably best in medium-traffic situations or when having each direction on different phases doesn't matter.
SPUIs and roundabouts have a bit of a learning curve. DDIs have less of one.
Driving on the wrong side of the road doesn't require a learning curve? I know if I hadn't read about Death Diamonds on the internet I would have turned right at the first traffic light into oncoming traffic. They are confusing, cheap (in the bad way) and will eventually prove to be deadly.
What is the learning curve for a SPUI? It functions much like a diamond and I don't see how they could cause confusion.
What are the operational benefits of a DDI compared to a PARCLO interchange? There are examples of full cloverleaf interchanges being converted to DDI's as opposed to PARCLO's (IE. I-79 & US19). A Parclo B4 has 12 conflict points as opposed to a DDI that has 14 conflict points. A Parclo B4 can achieve good coordination (since traffic signals only stop one-direction of travel) while a DDI you get bad coordination (since closely spaced traffic signals stop both directions of travel). Why crisscross traffic on US19 (and add two-additional conflict points) when PennDOT could simply take advantage of the grade separation between I-79 & US19 and turn it into a Parclo B4?
The DDI proposed at I-70 and US19 has roughly the same footprint as the full cloverleaf interchange that it's replacing.
http://www.i-70projects.com/docs/I70T20InterchangeLayoutFD%2004-03-14.pdf
Quote from: tradephoric on April 02, 2015, 11:09:48 AM
What are the operational benefits of a DDI compared to a PARCLO interchange? There are examples of full cloverleaf interchanges being converted to DDI's as opposed to PARCLO's (IE. I-79 & US19). A Parclo B4 has 12 conflict points as opposed to a DDI that has 14 conflict points. A Parclo B4 can achieve good coordination (since traffic signals only stop one-direction of travel) while a DDI you get bad coordination (since closely spaced traffic signals stop both directions of travel). Why crisscross traffic on US19 (and add two-additional conflict points) when PennDOT could simply take advantage of the grade separation between I-79 & US19 and turn it into a Parclo B4?
As was already mentioned, a DDI allows for I-70 to be widened without replacing the bridges. They're turning the auxiliary lane into an additional travel lane. Parclos are superior when space allows, but space isn't always available.
Quote from: bugo on April 02, 2015, 05:29:24 AM
Quote from: cl94 on March 30, 2015, 01:29:56 PM
From an engineering perspective, DDIs are superior to SPUIs in almost every case. While roundabouts are better in theory, people don't know how to use them. As previously stated, you only have to put down a little bit of concrete and change the striping and signals to get a major improvement, as both signals in the intersection are coordinated. Are they great when there are many adjacent intersections? No. But they are often many times better than the diamonds they replace. They're probably best in medium-traffic situations or when having each direction on different phases doesn't matter.
SPUIs and roundabouts have a bit of a learning curve. DDIs have less of one.
What is the learning curve for a SPUI? It functions much like a diamond and I don't see how they could cause confusion.
Tell that to people when one is first installed in an area. I-270 at Sawmill Rd in Columbus rings a very loud bell. There's a large amount of uncontrolled pavement and you have to get people to turn at the right places. When people are learning, it's a nightmare if not done with an excessive amount of signage.
Quote from: cl94 on April 02, 2015, 01:28:56 PM
Quote from: tradephoric on April 02, 2015, 11:09:48 AM
What are the operational benefits of a DDI compared to a PARCLO interchange? There are examples of full cloverleaf interchanges being converted to DDI's as opposed to PARCLO's (IE. I-79 & US19). A Parclo B4 has 12 conflict points as opposed to a DDI that has 14 conflict points. A Parclo B4 can achieve good coordination (since traffic signals only stop one-direction of travel) while a DDI you get bad coordination (since closely spaced traffic signals stop both directions of travel). Why crisscross traffic on US19 (and add two-additional conflict points) when PennDOT could simply take advantage of the grade separation between I-79 & US19 and turn it into a Parclo B4?
As was already mentioned, a DDI allows for I-70 to be widened without replacing the bridges. They're turning the auxiliary lane into an additional travel lane. Parclos are superior when space allows, but space isn't always available.
Your hung up on cost. I'll ask you another question. You say Parclo's are superior but there are different types of Parclos to choose from. Are there any operational, safety, or cost benefits of picking a Parclo A4 over a Parclo B4?
Quote from: bugo on April 02, 2015, 05:29:24 AM
What is the learning curve for a SPUI? It functions much like a diamond and I don't see how they could cause confusion.
I never understand why there's a learning curve with SPUIs at all. At traditional intersections, when opposing traffic makes a left turn, you each keep to the left. At a SPUI, when opposing traffic makes a left turn, you each keep to the left. The only difference is the starting angle is a bit different.
Quote from: bugo on April 02, 2015, 05:29:24 AM
Driving on the wrong side of the road doesn't require a learning curve? I know if I hadn't read about Death Diamonds on the internet I would have turned right at the first traffic light into oncoming traffic. They are confusing, cheap (in the bad way) and will eventually prove to be deadly.
Why would you have done that? Because the signage and pavement markings were unclear? Because the center median didn't establish a clear division of directions of traffic? Because you didn't understand the concept of a two-way street becoming a pair of one-way streets? Or because your future self spoke to you from this present reality and told you to make an incorrect maneuver, just to prove a point?
Quote from: bugo on April 02, 2015, 05:29:24 AM
...and will eventually prove to be deadly.
At what point while driving on a DDI are you travelling fast enough to die?
Quote from: tradephoric on April 02, 2015, 02:26:21 PM
Quote from: cl94 on April 02, 2015, 01:28:56 PM
Quote from: tradephoric on April 02, 2015, 11:09:48 AM
What are the operational benefits of a DDI compared to a PARCLO interchange? There are examples of full cloverleaf interchanges being converted to DDI's as opposed to PARCLO's (IE. I-79 & US19). A Parclo B4 has 12 conflict points as opposed to a DDI that has 14 conflict points. A Parclo B4 can achieve good coordination (since traffic signals only stop one-direction of travel) while a DDI you get bad coordination (since closely spaced traffic signals stop both directions of travel). Why crisscross traffic on US19 (and add two-additional conflict points) when PennDOT could simply take advantage of the grade separation between I-79 & US19 and turn it into a Parclo B4?
As was already mentioned, a DDI allows for I-70 to be widened without replacing the bridges. They're turning the auxiliary lane into an additional travel lane. Parclos are superior when space allows, but space isn't always available.
Your hung up on cost. I'll ask you another question. You say Parclo's are superior but there are different types of Parclos to choose from. Are there any operational, safety, or cost benefits of picking a Parclo A4 over a Parclo B4?
As an engineer, cost is a huge concern. No matter how much safety will improve, it won't get built if the cost is too high.
A4s are superior to B4s because A4 loops are entrance ramps and the freeway can take a constant influx of traffic better than a constrained surface facility. A properly designed Parclo is superior from a safety perspective, but not always from a cost perspective.
I admit that I've only driven on one DDI, but NYSDOT did a damn good job of making it clear with relatively little signage.
Quote from: bugo on April 02, 2015, 02:09:57 AM
The term "Death Diamond", coined by yours truly, has caught on in the road community.
It has? What community are you referring to? How many fatalities have been caused by this interchange type in the last 6 years?
Quote from: tradephoric on April 02, 2015, 02:26:21 PM
Your hung up on cost.
That's how it goes in the real world! Not impacting the bridge is a huge advantage.
Quote from: jakeroot on April 02, 2015, 07:40:59 PM
Quote from: bugo on April 02, 2015, 05:29:24 AM
...and will eventually prove to be deadly.
At what point while driving on a DDI are you travelling fast enough to die?
When you are driving fast enough for your car to split in half...
http://kfoxtv.com/news/features/top-stories/stories/Woman-killed-in-car-accident-after-hitting-splitting-car-in-half-in-East-El-Paso-61639.shtml#.VR3b244a6RM
Quote from: tradephoric on April 02, 2015, 08:44:13 PM
Quote from: jakeroot on April 02, 2015, 07:40:59 PM
Quote from: bugo on April 02, 2015, 05:29:24 AM
...and will eventually prove to be deadly.
At what point while driving on a DDI are you travelling fast enough to die?
When you are driving fast enough for your car to split in half...
http://kfoxtv.com/news/features/top-stories/stories/Woman-killed-in-car-accident-after-hitting-splitting-car-in-half-in-East-El-Paso-61639.shtml#.VR3b244a6RM
She was also believed to be drunk. Engineers can't prevent stupid.
Quote from: cl94 on April 02, 2015, 08:51:45 PM
Quote from: tradephoric on April 02, 2015, 08:44:13 PM
Quote from: jakeroot on April 02, 2015, 07:40:59 PM
Quote from: bugo on April 02, 2015, 05:29:24 AM
...and will eventually prove to be deadly.
At what point while driving on a DDI are you travelling fast enough to die?
When you are driving fast enough for your car to split in half...
http://kfoxtv.com/news/features/top-stories/stories/Woman-killed-in-car-accident-after-hitting-splitting-car-in-half-in-East-El-Paso-61639.shtml#.VR3b244a6RM
She was also believed to be drunk. Engineers can't prevent stupid.
What does it matter that the woman was drunk or not? Jake was asking a simple physics question. Can you answer this question?
Train A is traveling at 55 mph, and the conductor is piss drunk. How far will Train A travel if the conductor of Train B is having sex with a passenger?
Quote from: cl94 on April 02, 2015, 08:35:55 PM
Quote from: tradephoric on April 02, 2015, 02:26:21 PM
Quote from: cl94 on April 02, 2015, 01:28:56 PM
Quote from: tradephoric on April 02, 2015, 11:09:48 AM
What are the operational benefits of a DDI compared to a PARCLO interchange? There are examples of full cloverleaf interchanges being converted to DDI's as opposed to PARCLO's (IE. I-79 & US19). A Parclo B4 has 12 conflict points as opposed to a DDI that has 14 conflict points. A Parclo B4 can achieve good coordination (since traffic signals only stop one-direction of travel) while a DDI you get bad coordination (since closely spaced traffic signals stop both directions of travel). Why crisscross traffic on US19 (and add two-additional conflict points) when PennDOT could simply take advantage of the grade separation between I-79 & US19 and turn it into a Parclo B4?
As was already mentioned, a DDI allows for I-70 to be widened without replacing the bridges. They're turning the auxiliary lane into an additional travel lane. Parclos are superior when space allows, but space isn't always available.
Your hung up on cost. I'll ask you another question. You say Parclo's are superior but there are different types of Parclos to choose from. Are there any operational, safety, or cost benefits of picking a Parclo A4 over a Parclo B4?
As an engineer, cost is a huge concern. No matter how much safety will improve, it won't get built if the cost is too high.
Is the cost of each interchange design relevant to the question i asked? Even if a DDI interchange is less costly than a PARCLO, how do i know that the savings are worth it if the operational benefits aren't known? Maybe the DDI is a guaranteed piece of SHIT!
https://www.youtube.com/watch?v=a5dpBpaFiMo
Modified DDIs have existed for a while, not including 40 year old DDIs in France. Take I-95 Exit 18 in Rhode Island. It's really no different than a one-way pair (which is exactly how it functions). So far, in the 6 years they've existed in the US, there haven't been many major issues. Speed isn't as much of an issue because they're not meant to be used on high-speed roadways. They're a simple solution with little construction and, if major problems become apparent, they can be reverted to standard diamonds with little effort.
We understand that you don't like the idea. Engineering studies have shown that the design can be effective and increase efficiency when replacing other designs.
Quote from: tradephoric on April 02, 2015, 09:39:39 PM
Train A is traveling at 55 mph, and the conductor is piss drunk. How far will Train A travel if the conductor of Train B is having sex with a passenger?
A long way. Drink provokes the desire, but it takes away the performance.
Quote from: cl94 on April 02, 2015, 11:15:51 PM
Engineering studies have shown that the design [DDI's] can be effective and increase efficiency when replacing other designs.
The flip side is DDI's can decrease efficiency when replacing "other designs". Your sentence is fluff when you don't define what the other designs are. Feel free to cite these phantom engineering studies.
Quote from: tradephoric on April 02, 2015, 09:39:39 PM
^Whether or not the woman was drunk is irrelevant to Jake's question. It's a simple physics question he's after. Physics questions on testQuote from: cl94 on April 02, 2015, 08:51:45 PM
Quote from: tradephoric on April 02, 2015, 08:44:13 PM
Quote from: jakeroot on April 02, 2015, 07:40:59 PM
Quote from: bugo on April 02, 2015, 05:29:24 AM
...and will eventually prove to be deadly.
At what point while driving on a DDI are you travelling fast enough to die?
When you are driving fast enough for your car to split in half...
http://kfoxtv.com/news/features/top-stories/stories/Woman-killed-in-car-accident-after-hitting-splitting-car-in-half-in-East-El-Paso-61639.shtml#.VR3b244a6RM
She was also believed to be drunk. Engineers can't prevent stupid.
What does it matter that the woman was drunk or not? Jake was asking a simple physics question.
Allow me to rephrase: "At what point while driving on a DDI are everyday citizens, who are paying attention to the road and not driving distracted or too quickly, travelling fast enough to die?"
A normal, everyday citizen (i.e. those
not drinking/driving distracted/driving too fast for conditions) should not have any problems navigating a DDI. The death was because of her apparent intoxication, not the engineering of the junction. As cl94 said, engineers can't prevent stupid.
Quote from: tradephoric on April 02, 2015, 08:44:13 PM
Quote from: jakeroot on April 02, 2015, 07:40:59 PM
Quote from: bugo on April 02, 2015, 05:29:24 AM
...and will eventually prove to be deadly.
At what point while driving on a DDI are you travelling fast enough to die?
When you are driving fast enough for your car to split in half...
http://kfoxtv.com/news/features/top-stories/stories/Woman-killed-in-car-accident-after-hitting-splitting-car-in-half-in-East-El-Paso-61639.shtml#.VR3b244a6RM
Not exactly an argument against the general concept of a DDI though, considering a full on freeway terminates at this one. Some drunk old lady doing 60 through the original diamond probably would have had a much worse result T-boning someone else. Maybe a DDI isn't the greatest choice for a freeway to freeway interchange, but there aren't a lot of alternatives that don't involve expensive flyovers or tearing down the existing freeway.
Quote from: stridentweasel on April 02, 2015, 05:46:05 PM
Quote from: bugo on April 02, 2015, 05:29:24 AM
Driving on the wrong side of the road doesn't require a learning curve? I know if I hadn't read about Death Diamonds on the internet I would have turned right at the first traffic light into oncoming traffic. They are confusing, cheap (in the bad way) and will eventually prove to be deadly.
Why would you have done that? Because the signage and pavement markings were unclear? Because the center median didn't establish a clear division of directions of traffic? Because you didn't understand the concept of a two-way street becoming a pair of one-way streets? Or because your future self spoke to you from this present reality and told you to make an incorrect maneuver, just to prove a point?
Because of the tendency to stay on the right (*correct*) side of the road which happens to be the right side. Crossing over to the left is inherently more dangerous than staying on the right is.
The Death Diamond is nothing more than a cheap "solution" to a problem that usually doesn't exist. I've driven through the MO 13/I-44 interchange before and after it was converted and I didn't see any improvement after it was converted to a Death Diamond. Build a proper interchange or leave the diamond the fuck alone. An even better solution would have been to put frontage roads along I-44 and use slip ramps to go to and from the frontage road to the mainline. Sure it would be more expensive than a Death Diamond but hey, you get what you pay for.
Yo Hibby, 'death diamond' is bugo's term for roundabout. Go make out in the hay.
Having never driven through a DDI: what kind of an angle would the "wrong way" right turn be? It seems like a driver would be close to making a 90o right turn in order to stay on the right. In other words, if a driver comes to the first signal, they are going to just go straight across at the intersection - and likely not even realize they're on the wrong side of the road until they are actually into the DDI.
Quote from: jakeroot link=topic=15118.msg2055124#msg2055124
"At what point while driving on a DDI are everyday citizens, who are paying attention to the road and not driving distracted or too quickly, travelling fast enough to die?"
A normal, everyday citizen (i.e. those not drinking/driving distracted/driving too fast for conditions) should not have any problems navigating a DDI. The death was because of her apparent intoxication, not the engineering of the junction. As cl94 said, engineers can't prevent stupid.
It's stupid to assume that a sober driver traveling safely through a DDI is immune to other people's stupidity. The crossing angle at a DDI has a high angle of incidence which is one of the disadvantages of the design. A drunk driver blowing through a red light at a DDI is susceptible to being involved in a near head on crash. You can't stop stupid but you can try to limit its effects.
Quote from: bugo on April 03, 2015, 09:02:04 AM
Quote from: stridentweasel on April 02, 2015, 05:46:05 PM
Quote from: bugo on April 02, 2015, 05:29:24 AM
Driving on the wrong side of the road doesn't require a learning curve? I know if I hadn't read about Death Diamonds on the internet I would have turned right at the first traffic light into oncoming traffic. They are confusing, cheap (in the bad way) and will eventually prove to be deadly.
Why would you have done that? Because the signage and pavement markings were unclear? Because the center median didn't establish a clear division of directions of traffic? Because you didn't understand the concept of a two-way street becoming a pair of one-way streets? Or because your future self spoke to you from this present reality and told you to make an incorrect maneuver, just to prove a point?
Because of the tendency to stay on the right (*correct*) side of the road which happens to be the right side.
England and other left-hand drive countries disagree.
QuoteCrossing over to the left is inherently more dangerous than staying on the right is.
I-5 through the Grapevine disagrees. As do a few full-freeway interchanges that feature DDI type interchanges (though they do have the 'weaknesses' of left-hand exits and entrances).
You wear your bias on your sleeve calling it a 'Death Diamond' when there's no evidence the term's warranted outside of a ski resort.
Quote from: tradephoric on April 03, 2015, 10:12:37 AM
The crossing angle at a DDI has a high angle of incidence which is one of the disadvantages of the design.
The FHWA's (albeit small) study on "Drivers' Evaluation of the Diverging Diamond Interchange (http://www.fhwa.dot.gov/publications/research/safety/07048/)" reported that none of the participants performed a wrong-way manoeuvre at the crossover point. There were wrong-way manoeuvers whereby an elderly driver repeatedly turned left onto the offramp after the initial crossover, but they attribute this error to poor signing.
Obviously you're quoting a more recent study...if you could please provide a link, I'd love to read it.
Quote from: jakeroot on April 03, 2015, 12:17:05 PM
Quote from: tradephoric on April 03, 2015, 10:12:37 AM
The crossing angle at a DDI has a high angle of incidence which is one of the disadvantages of the design.
The FHWA's (albeit small) study on "Drivers' Evaluation of the Diverging Diamond Interchange (http://www.fhwa.dot.gov/publications/research/safety/07048/)" reported that none of the participants performed a wrong-way manoeuvre at the crossover point. There were wrong-way manoeuvers whereby an elderly driver repeatedly turned left onto the offramp after the initial crossover, but they attribute this error to poor signing.
Obviously you're quoting a more recent study...if you could please provide a link, I'd love to read it.
(https://www.aaroads.com/forum/proxy.php?request=http%3A%2F%2Fwww.fhwa.dot.gov%2Fpublications%2Fresearch%2Fsafety%2F07048%2Fimages%2Ffig2.gif&hash=4c24f94296750cfe351197ed11d2f948c9a84455)
If two drivers going in opposite directions travel through a crossing conflict point of a DDI intersection, the angle of the two vehicles striking would be nearly head on. Put another way, the crossing angle at a DDI has a high angle of incidence Do i really need to cite a study to make that point?
My interest is comparing the operational differences between a DDI and a PARCLO. You cite a study that compares a DDI to a diamond. Don't feel obligated to answer a question that you don't have the answer to. I readily admit i don't know the operational differences between a DDI and a PARCLO. That's why i keep asking the question (probably to the annoyance of some, but ooh well). Cite me that study and I'll be happy!
Except the angle of incidence thing is relatively inapplicable to this situation because they're 2 one way streets that just happen to cross without a single turn movement and you can see traffic in the opposing direction.
We don't know the differences between a DDI and a parclo because they're intended for different situations. Will there be a study? Possibly. But as of now, they're not considered to be comparable.
DDI in St. George, Utah:(https://www.aaroads.com/forum/proxy.php?request=http%3A%2F%2Ffarm6.staticflickr.com%2F5543%2F10970371923_60c699d365_b.jpg&hash=e0a43eb7d92d017f424ede1acdfeb93dfe119952)
QuoteUDOT DIVERGING DIAMOND INTERCHANGE (DDI) OBSERVATIONS AND EXPERIENCE:
Coordination of the DDI with adjacent signals is not easily done. Most DDIs need a lower cycle length than the adjacent signals. This may result in a vehicle having to stop at both the off ramp terminal and the next adjacent signal.
The closest adjacent signal to the St. George DDI is 550 feet away (roughly an 8 second travel time at 45 mph). Who wants to get a green light only to come to a red light 8 second later? That's the epitome of inefficiency. In the picture you see roughly 20 cars needlessly waiting at a red light... no opposing traffic, just lots of dead air.
That's a red herring argument, as signals all over the place are ill timed or have needless phases. It's not unique to DDIs at all.
Quote from: Bickendan on April 03, 2015, 02:16:26 PM
That's a red herring argument, as signals all over the place are ill timed or have needless phases. It's not unique to DDIs at all.
That's like telling a 600 lbs guy to keep eating 12,000 calories a day since they are already morbidly obese.
If most traffic is turning (as should happen if a DDI is warranted), the problem exists no matter what type of interchange you have.
Quote from: Bickendan on April 03, 2015, 02:16:26 PM
That's a red herring argument, as signals all over the place are ill timed or have needless phases. It's not unique to DDIs at all.
They can be timed very well. However, DDIs don't help; Michigan Lefts do.
DDIs are bad when there are adjacent intersections within a short distance. We know that. In that case, a SPUI is better. That's one of the few cases where a SPUI will outperform a DDI, as signals can be coordinated. A DDI in the location you posted is a poor choice for that reason, but there may have been other factors.
Quote from: tradephoric on April 03, 2015, 02:00:47 PM
DDI in St. George, Utah:
(https://www.aaroads.com/forum/proxy.php?request=http%3A%2F%2Ffarm6.staticflickr.com%2F5543%2F10970371923_60c699d365_b.jpg&hash=e0a43eb7d92d017f424ede1acdfeb93dfe119952)
QuoteUDOT DIVERGING DIAMOND INTERCHANGE (DDI) OBSERVATIONS AND EXPERIENCE:
Coordination of the DDI with adjacent signals is not easily done. Most DDIs need a lower cycle length than the adjacent signals. This may result in a vehicle having to stop at both the off ramp terminal and the next adjacent signal.
The closest adjacent signal to the St. George DDI is 550 feet away (roughly an 8 second travel time at 45 mph). Who wants to get a green light only to come to a red light 8 second later? That's the epitome of inefficiency. In the picture you see roughly 20 cars needlessly waiting at a red light... no opposing traffic, just lots of dead air.
The heaviest movement of Eastbound St George Blvd - Northbound I-15 is favored by that intersection, and from what I saw when I drove it, it seemed to work rather well, as long as you can get through the first crossover signal. It also seemed to work well five years ago when it was a normal diamond. I never drove it during rush hour. Maybe someone from the area can chime in...
Quote from: cl94 on April 03, 2015, 06:54:28 PM
DDIs are bad when there are adjacent intersections within a short distance. We know that. In that case, a SPUI is better. That's one of the few cases where a SPUI will outperform a DDI, as signals can be coordinated. A DDI in the location you posted is a poor choice for that reason, but there may have been other factors.
Coordinating traffic signals doesn't necessarily lead to improvements in progression. Here is an example of a Parclo A4 interchange at HWY 410 & Steeles Avenue in Toronto (the red icons represent traffic signals that stop both directions of travel):
(https://www.aaroads.com/forum/proxy.php?request=http%3A%2F%2Fi478.photobucket.com%2Falbums%2Frr144%2Ftradephoric%2FTransportation%2520Pictures%2FRandom%2FToronto410interchange-1.jpg&hash=d81ae054d1f80d25e39e22ebdaa802e2932e1f26)
(https://www.aaroads.com/forum/proxy.php?request=http%3A%2F%2Fi478.photobucket.com%2Falbums%2Frr144%2Ftradephoric%2FTransportation%2520Pictures%2FRandom%2FTorontoArterialnon-superstreet.jpg&hash=98bce2d341b6d9c9f8bcd9f37949785520641c00)
The signals are coordinated yet progression still sucks. Providing perfect progression in one-direction leads to green-to-red progression in the other. Whenever you have closely spaced traffic signals that stop both directions of travel, progression will suffer. A coordinated SPUI might be as ineffective as an uncoordinated DDI in that Utah example i posted.
Quote from: Bickendan on April 03, 2015, 02:16:26 PM
That's a red herring argument, as signals all over the place are ill timed or have needless phases. It's not unique to DDIs at all.
Timing a corridor for good signal progression is a skill lost in history, like Egyptian pyramid-building techniques. Detroit is clinging on to the lost skill, but as progression killing designs like DDIs and SPUIs emerge their efforts may prove futile. Enjoy the good signal progression while it lasts...
https://www.youtube.com/watch?v=oea5WLUmGjs
Quote from: tradephoric on April 04, 2015, 04:29:54 PM
Timing a corridor for good signal progression is a skill lost in history, like Egyptian pyramid-building techniques. Detroit is clinging on to the lost skill, but as progression killing designs like DDIs and SPUIs emerge their efforts may prove futile. Enjoy the good signal progression while it lasts...
Eh, most interchanges are difficult to time, especially with high turning movement. Its not like diamond interchanges are any better. Only solutions that are better is using all ramps. Even in that video, when they were near an interchange towards the end, they had to stop. SPUI should be way better than a standard diamond as far as progression, no?
If you have free-flow ramps for entering onto the surface road, you need to deal with weaving (i.e. people who want to turn left immediately).
Quote from: UCFKnights on April 04, 2015, 05:20:22 PM
Quote from: tradephoric on April 04, 2015, 04:29:54 PM
Timing a corridor for good signal progression is a skill lost in history, like Egyptian pyramid-building techniques. Detroit is clinging on to the lost skill, but as progression killing designs like DDIs and SPUIs emerge their efforts may prove futile. Enjoy the good signal progression while it lasts...
Eh, most interchanges are difficult to time, especially with high turning movement. Its not like diamond interchanges are any better. Only solutions that are better is using all ramps. Even in that video, when they were near an interchange towards the end, they had to stop. SPUI should be way better than a standard diamond as far as progression, no?
How does the signal progression look at this SPUI...
(https://www.aaroads.com/forum/proxy.php?request=http%3A%2F%2Fi478.photobucket.com%2Falbums%2Frr144%2Ftradephoric%2FTransportation%2520Pictures%2FRandom%2FSPUITelegraph_zpsko5aaf5f.png&hash=709e3b94a24f9b3a97c271fe40c56134b3c53bc1) (http://s478.photobucket.com/user/tradephoric/media/Transportation%20Pictures/Random/SPUITelegraph_zpsko5aaf5f.png.html)
That SPUI has EWWY signal progression. This is not an atypical scenario. Many SPUIs will have corridors running 45 mph at 120 second cycle lengths and adjacent signals spaced roughly 1500 feet apart. The SPUI stops both directions of travel along the corridor killing progression.
I don't disagree that most interchanges are difficult to time. That's because most interchange signals stop
BOTH DIRECTIONS OF TRAFFIC! The solution? Choose interchange designs where the signals only stop
ONE DIRECTION OF TRAFFIC!! That's it! :clap:
Quote from: NE2 on April 04, 2015, 06:20:34 PM
If you have free-flow ramps for entering onto the surface road, you need to deal with weaving (i.e. people who want to turn left immediately).
Accidents caused by weaving cause less bodily and financial harm. I should hope, too, that some immediate left turns could be prevented with raised medians.
Quote from: tradephoric on April 05, 2015, 02:05:46 AM
I don't disagree that most interchanges are difficult to time. That's because most interchange signals stop BOTH DIRECTIONS OF TRAFFIC! The solution? Choose interchange designs where the signals only stop ONE DIRECTION OF TRAFFIC!! That's it! :clap:
I'd love to know the numbers on the I-5/S 38th Street interchange in Tacoma, Washington. It's a parclo B4. Traffic flow is always steady ... very little waiting at any of the signals (though it does help that, in Washington, I can turn left onto the on-ramp after a stop).
(https://www.aaroads.com/forum/proxy.php?request=http%3A%2F%2Fi478.photobucket.com%2Falbums%2Frr144%2Ftradephoric%2FTransportation%2520Pictures%2FRandom%2FSPUIfootprint_zpsmzdltffn.png&hash=cb4236172c6e166cf49f941e1da8311797c8443e)
The SPUI at I-94 & Telegraph has a larger footprint than the Parclo B4 at I-75 & 14 Mile. MDOT, in their infinite wisdom, decided a progression killing SPUI would work better than a progression saving Parclo B4 at I-94 & Telegraph.
No, it's that a parclo with modern curve radii wouldn't have fit in the area occupied by the effed-up interchange it replaced while providing little improvement. And what's with the obsession over B4s? They're the worst type of parclo to have because there's unrestricted flow onto the surface road.
Quote from: NE2 on April 04, 2015, 06:20:34 PM
If you have free-flow ramps for entering onto the surface road, you need to deal with weaving (i.e. people who want to turn left immediately).
Worst case you could always modify the loop ramps to be signal controlled instead of free-flow.
Quote from: cl94They're the worst type of parclo to have because there's unrestricted flow onto the surface road.
As a budding engineer, surely you realize that how the unrestricted flow affects the surface road will depend on the volume of that flow and the location/design of downstream impediments on the surface road.
Furthermore, one point about B4's that hasn't been made yet is that they only require ONE signal per direction for through movement on the surface road, vice two for an A4.
In rural situations, a safety case can also be made for a B4 over an A4. In a B4, non-loop turning traffic only needs to worry about traffic from one direction on the surface-road (namely the oncoming traffic). In an A4, the non-loop turning traffic has to watch for BOTH directions on the surface-road.
Quote from: tradephoric on April 05, 2015, 12:49:06 PM
(https://www.aaroads.com/forum/proxy.php?request=http%3A%2F%2Fi478.photobucket.com%2Falbums%2Frr144%2Ftradephoric%2FTransportation%2520Pictures%2FRandom%2FSPUIfootprint_zpsmzdltffn.png&hash=cb4236172c6e166cf49f941e1da8311797c8443e)
The SPUI at I-94 & Telegraph has a larger footprint than the Parclo B4 at I-75 & 14 Mile. MDOT, in their infinite wisdom, decided a progression killing SPUI would work better than a progression saving Parclo B4 at I-94 & Telegraph.
Your measurements included portions of the freeway itself, as well as the surface road, which would be there even without an interchange. Importantly, you included greater length of freeway for the SPUI, possibly tipping the area comparison. To make an effective real estate comparison, do not include areas that would be within highway ROW without any interchange.
Quote from: cl94 on April 05, 2015, 01:43:11 PM
No, it's that a parclo with modern curve radii wouldn't have fit in the area occupied by the effed-up interchange it replaced while providing little improvement. And what's with the obsession over B4s? They're the worst type of parclo to have because there's unrestricted flow onto the surface road.
Signalize the off-ramps so there's not unrestricted flow then. Revive 755 already touched on this simple solution. Here's an example of a Parclo B4 in Florida with signalized off-ramps:
https://www.google.com/maps/@26.007247,-80.3406062,709m/data=!3m1!1e3
Note: I-75 & Pines Blvd use to have unrestricted flow onto the surface road but the interchange was reconfigured around 2009 to signalize the off-ramps.
Question: Is signal progression actually a consideration that agencies make when deciding between different interchange configurations?
I know we like to think of a solution as "good" of we can personally drive through it with zero or one red light, and likewise "bad" if we can personally drive through it with what we feel are unnecessary stops. But traffic needs in the bigger picture are much more complex, and the best solution doesn't always mean what we think it might.
Quote from: tradephoric on April 05, 2015, 12:49:06 PM
(https://www.aaroads.com/forum/proxy.php?request=http%3A%2F%2Fi478.photobucket.com%2Falbums%2Frr144%2Ftradephoric%2FTransportation%2520Pictures%2FRandom%2FSPUIfootprint_zpsmzdltffn.png&hash=cb4236172c6e166cf49f941e1da8311797c8443e)
The SPUI at I-94 & Telegraph has a larger footprint than the Parclo B4 at I-75 & 14 Mile. MDOT, in their infinite wisdom, decided a progression killing SPUI would work better than a progression saving Parclo B4 at I-94 & Telegraph.
Well, M-DOT wasted a lot of money. They moved from a free-flowing, left exiting system that worked and handled the traffic, to a non-free flowing system that can't. Even the parclo would have been worse than leaving 94/24 alone.
Quote from: tradephoric on April 05, 2015, 02:47:57 PM
Signalize the off-ramps so there's not unrestricted flow then. Revive 755 already touched on this simple solution. Here's an example of a Parclo B4 in Florida with signalized off-ramps:
WSDOT does that a lot. It bugs me, since I've always thought that Parclos should look like the kind that Ontario builds (with proper curves, etc). But, seeing the reason, I'm less put-off.
Quote from: tradephoric on April 03, 2015, 02:00:47 PM
DDI in St. George, Utah:
(https://www.aaroads.com/forum/proxy.php?request=http%3A%2F%2Ffarm6.staticflickr.com%2F5543%2F10970371923_60c699d365_b.jpg&hash=e0a43eb7d92d017f424ede1acdfeb93dfe119952)
QuoteUDOT DIVERGING DIAMOND INTERCHANGE (DDI) OBSERVATIONS AND EXPERIENCE:
Coordination of the DDI with adjacent signals is not easily done. Most DDIs need a lower cycle length than the adjacent signals. This may result in a vehicle having to stop at both the off ramp terminal and the next adjacent signal.
The closest adjacent signal to the St. George DDI is 550 feet away (roughly an 8 second travel time at 45 mph). Who wants to get a green light only to come to a red light 8 second later? That's the epitome of inefficiency. In the picture you see roughly 20 cars needlessly waiting at a red light... no opposing traffic, just lots of dead air.
They say a picture is worth a thousand words. Sometimes, those words are wrong.
A picture is simply a single point in time. I could sit atop a building for hours, wait for the perfect moment, snap a picture, and develop an entire story around that one moment in time. Nevermind pictures that I could've snapped every second for several hours would've revealed something else.
While it appears the traffic is waiting there for air, there's also traffic at the bottom of the picture. That traffic may had just made it thru the intersection, and the signal simply didn't cycle thru for the green light yet. Looking at the red pickup with the trailer - he certainly seems to be someone moving. He may have just went thru that intersection a second earlier, justifying the red light and the waiting traffic.
And in a construction zone, signals are rarely optimized for the most efficient flow of traffic. Traffic detectors may still need to be installed and programmed. Traffic shifts and lane closures frequently happen. It's fairly clear there's little if any signage in place.
If you want to criticize a DDI because of this picture, I'll just pull up photos of traffic sitting at red lights at all sorts of intersections. Even the most optimized traffic corridors won't have free-flowing traffic 100% of the time.
Quote from: jeffandnicole on April 06, 2015, 09:01:46 AMThey say a picture is worth a thousand words. Sometimes, those words are wrong.
A picture is simply a single point in time. I could sit atop a building for hours, wait for the perfect moment, snap a picture, and develop an entire story around that one moment in time. Nevermind pictures that I could've snapped every second for several hours would've revealed something else.
While it appears the traffic is waiting there for air, there's also traffic at the bottom of the picture. That traffic may had just made it thru the intersection, and the signal simply didn't cycle thru for the green light yet. Looking at the red pickup with the trailer - he certainly seems to be someone moving. He may have just went thru that intersection a second earlier, justifying the red light and the waiting traffic.
And in a construction zone, signals are rarely optimized for the most efficient flow of traffic. Traffic detectors may still need to be installed and programmed. Traffic shifts and lane closures frequently happen. It's fairly clear there's little if any signage in place.
If you want to criticize a DDI because of this picture, I'll just pull up photos of traffic sitting at red lights at all sorts of intersections. Even the most optimized traffic corridors won't have free-flowing traffic 100% of the time.
A picture is worth a thousand words and a time-distance diagram is worth ten thousand. You're fooling yourself if you can't acknowledge that DDIs, SPUIs and Parclo A4s lead to poor signal progression along a corridor. Closely spaced traffic signals that stop both directions of travel along a corridor will lead to poor signal progression. That's exactly what you get with a DDI.
I for one believe drivers get stopped at way too many red lights and DDIs compound the problem.
Yawn. DDIs are not intended for interchanges where the majority of surface traffic does not enter or exit the freeway. Therefore signal progression has no meaning when considering a DDI.
Quote from: NE2 on April 06, 2015, 10:14:34 AM
Yawn. DDIs are not intended for interchanges where the majority of surface traffic does not enter or exit the freeway. Therefore signal progression has no meaning when considering a DDI.
There are hundreds of SPUIs and Parclo A4s where good progression along the corridor should be a key concern. However, these designs also stop both directions of travel and suffer from poor signal progression. I know this thread was originally about DDIs but it has morphed into interchange designs that lead to poor signal progression (SPUIs and Parclo A4s included). The point you are making in regards to DDIs can't be applied to the hundreds of SPUIs and Parclo A4s out there.
Don't you want to drive 10, 15, or 20 miles along a major corridor and never get stopped at a red light? Good progression is lost when progression killing interchange designs are chosen (ie. DDIs, SPUIs, & PARCLO A4s).
Quote from: tradephoric on April 06, 2015, 11:03:36 AM
Don't you want to drive 10, 15, or 20 miles along a major corridor and never get stopped at a red light?
That would be nice, but lights are rarely timed for bike speeds.
Quote from: NE2 on April 06, 2015, 11:05:57 AM
Quote from: tradephoric on April 06, 2015, 11:03:36 AM
Don't you want to drive 10, 15, or 20 miles along a major corridor and never get stopped at a red light?
That would be nice, but lights are rarely timed for bike speeds.
This. You need a one-way grid for it to work, and even in downtown Portland, the signal timing leaves a bit to be desired.
Quote from: Bickendan on April 06, 2015, 11:10:46 AM
Quote from: NE2 on April 06, 2015, 11:05:57 AM
Quote from: tradephoric on April 06, 2015, 11:03:36 AM
Don't you want to drive 10, 15, or 20 miles along a major corridor and never get stopped at a red light?
That would be nice, but lights are rarely timed for bike speeds.
This. You need a one-way grid for it to work, and even in downtown Portland, the signal timing leaves a bit to be desired.
Getting off topic, but here is downtown Portland's grid in action. The city has very condensed grid so the 'green wave' that achieves perfect progression is only 12 mph (at 56 second cycle lengths). A driver is pretty much limited to driving 12 mph through downtown Portland.
https://www.youtube.com/watch?v=4mlZMPqJBLE
https://www.youtube.com/watch?v=7jGWdCknurM
Quote from: tradephoric on April 06, 2015, 11:03:36 AM
Quote from: NE2 on April 06, 2015, 10:14:34 AM
Yawn. DDIs are not intended for interchanges where the majority of surface traffic does not enter or exit the freeway. Therefore signal progression has no meaning when considering a DDI.
There are hundreds of SPUIs and Parclo A4s where good progression along the corridor should be a key concern. However, these designs also stop both directions of travel and suffer from poor signal progression. I know this thread was originally about DDIs but it has morphed into interchange designs that lead to poor signal progression (SPUIs and Parclo A4s included). The point you are making in regards to DDIs can't be applied to the hundreds of SPUIs and Parclo A4s out there.
Don't you want to drive 10, 15, or 20 miles along a major corridor and never get stopped at a red light? Good progression is lost when progression killing interchange designs are chosen (ie. DDIs, SPUIs, & PARCLO A4s).
Timing lights to hit nothing but green along major corridors of these lengths is fairly unrealistic. In a rural area, there's going to be too many varying speed differences to program the lights to offset from one another. Even if you program the lights for the speed limit, chances are people will go above or below that limit. In a suburban or urban setting, there's too many people entering and exiting driveways, parking lots, etc. And eventually you're going to come along an opposing major corridor which is going to require a different light sequence than the corridor you're on.
If you can get a few miles of good signal coordination, I'll be happy with that. 10 miles with a few reds isn't too bad. But to expect to go 20 miles with nothing but green lights is a near impossible feat.
Quote from: jeffandnicole on April 06, 2015, 12:00:37 PM
Timing lights to hit nothing but green along major corridors of these lengths is fairly unrealistic. In a rural area, there's going to be too many varying speed differences to program the lights to offset from one another. Even if you program the lights for the speed limit, chances are people will go above or below that limit. In a suburban or urban setting, there's too many people entering and exiting driveways, parking lots, etc. And eventually you're going to come along an opposing major corridor which is going to require a different light sequence than the corridor you're on.
There have already been 3 videos posted in this thread demonstrating good two-way signal progression. All of these corridors are found in Metro Detroit. You won't see any progression killing DDIs, SPUIs, or Parclo A4s in these videos...
https://www.youtube.com/watch?v=eB2H4bGp4Jc
https://www.youtube.com/watch?v=7hvUm9vYJYI
https://www.youtube.com/watch?v=oea5WLUmGjs
Quote from: jeffandnicole on April 06, 2015, 12:00:37 PMIf you can get a few miles of good signal coordination, I'll be happy with that. 10 miles with a few reds isn't too bad. But to expect to go 20 miles with nothing but green lights is a near impossible feat.
Traveling 20 miles on US-24 without hitting a red light. There is a caveat though as only the first 10 miles is capable of good two-way signal progression.
https://www.youtube.com/watch?v=Wkf7iLSblZ0
Quote from: tradephoric on April 06, 2015, 11:33:36 AM
Quote from: Bickendan on April 06, 2015, 11:10:46 AM
Quote from: NE2 on April 06, 2015, 11:05:57 AM
Quote from: tradephoric on April 06, 2015, 11:03:36 AM
Don't you want to drive 10, 15, or 20 miles along a major corridor and never get stopped at a red light?
That would be nice, but lights are rarely timed for bike speeds.
This. You need a one-way grid for it to work, and even in downtown Portland, the signal timing leaves a bit to be desired.
Getting off topic, but here is downtown Portland's grid in action. The city has very condensed grid so the 'green wave' that achieves perfect progression is only 12 mph (at 56 second cycle lengths). A driver is pretty much limited to driving 12 mph through downtown Portland.
On most days, I cycle more miles than I drive. Under both circumstances in a dense urban district, I would much prefer to move peacefully along at a steady 12 or 15 m.p.h. than be constantly starting and stopping.
Quote from: tradephoric on April 06, 2015, 12:25:31 PMThere have already been 3 videos posted in this thread demonstrating good two-way signal progression. All of these corridors are found in Metro Detroit.
Made possible by the fact that Detroit's arterials are nearly all mile-grid roads with Michigan Lefts. How much of Boston or Atlanta would have to be demolished to make room for such a neat road system that is so agreeable to signal progression?
PS – I can imagine in my head some time/distance diagrams demonstrating SPUIs and A4s that don't ruin signal progression in a Detroit-like arterial grid. It wouldn't be perfect, and it would be highly dependent on the geometry being a certain way, (which is already a requirement for the kind of progression that gets tradephoric off), but it's possible. If I feel like sacrificing some of my free time for the task, I may share these diagrams in the next couple of days.
Quote from: vtk on April 06, 2015, 01:46:13 PM
Made possible by the fact that Detroit's arterials are nearly all mile-grid roads with Michigan Lefts. How much of Boston or Atlanta would have to be demolished to make room for such a neat road system that is so agreeable to signal progression?
If signal progression is already bad, like in the case of Boston or Atlanta, wouldn't that be a good reason to choose interchange designs that improve upon progression? If someone is drowning would you try to hold their head under the water?
Quote from: tradephoric on April 06, 2015, 02:44:21 PM
Quote from: vtk on April 06, 2015, 01:46:13 PM
Made possible by the fact that Detroit's arterials are nearly all mile-grid roads with Michigan Lefts. How much of Boston or Atlanta would have to be demolished to make room for such a neat road system that is so agreeable to signal progression?
If signal progression is already bad, like in the case of Boston or Atlanta, wouldn't that be a good reason to choose interchange designs that improve upon progression? If someone is drowning would you try to hold their head under the water?
No, it doesn't work like that, and you missed my point. Unless you completely reconfigure the arterial network on a large scale in cities like that, the best signal progression that's even possible is still hardly recognizable as any progression at all. Sure, a choice between interchange designs may have an impact on signal progression, but we're probably talking about two nearly indistinguishable shades of crap, compared to Metro Detroit.
If someone's drowning, do you fuss over whether it's Lake Erie water or Evian that they are drowning in?
Quote from: vtk on April 06, 2015, 02:54:52 PM
Quote from: tradephoric on April 06, 2015, 02:44:21 PM
Quote from: vtk on April 06, 2015, 01:46:13 PM
Made possible by the fact that Detroit's arterials are nearly all mile-grid roads with Michigan Lefts. How much of Boston or Atlanta would have to be demolished to make room for such a neat road system that is so agreeable to signal progression?
If signal progression is already bad, like in the case of Boston or Atlanta, wouldn't that be a good reason to choose interchange designs that improve upon progression? If someone is drowning would you try to hold their head under the water?
No, it doesn't work like that, and you missed my point. Unless you completely reconfigure the arterial network on a large scale in cities like that, the best signal progression that's even possible is still hardly recognizable as any progression at all. Sure, a choice between interchange designs may have an impact on signal progression, but we're probably talking about two nearly indistinguishable shades of crap, compared to Metro Detroit.
If someone's drowning, do you fuss over whether it's Lake Erie water or Evian that they are drowning in?
Thank you. Interchange design in much of the world is designed to get people onto the limited-access road as fast as possible, thus removing traffic from surface streets. This is the best design if arterials are clogged and the freeway has capacity, as you're minimizing traffic that backs up on the surface road.
What works in one place doesn't necessarily work everywhere. Understand that.
Quote from: cl94 on April 06, 2015, 03:02:38 PM
Interchange design in much of the world is designed to get people onto the limited-access road as fast as possible, thus removing traffic from surface streets. This is the best design if arterials are clogged and the freeway has capacity, as you're minimizing traffic that backs up on the surface road.
But weren't freeways sort of designed as bypass roads? If you introduce too much local traffic onto them, you get congestion on the freeway.
I understand how people often use freeways, but to me, they should be used to go from A to C by bypassing B, not to go from A to B to C (in the former, you can still access C, but you must exit at an arterial and drive the extra distance).
Quote from: vtk on April 06, 2015, 02:54:52 PM
Quote from: tradephoric on April 06, 2015, 02:44:21 PM
Quote from: vtk on April 06, 2015, 01:46:13 PM
Made possible by the fact that Detroit's arterials are nearly all mile-grid roads with Michigan Lefts. How much of Boston or Atlanta would have to be demolished to make room for such a neat road system that is so agreeable to signal progression?
If signal progression is already bad, like in the case of Boston or Atlanta, wouldn't that be a good reason to choose interchange designs that improve upon progression? If someone is drowning would you try to hold their head under the water?
No, it doesn't work like that, and you missed my point. Unless you completely reconfigure the arterial network on a large scale in cities like that, the best signal progression that's even possible is still hardly recognizable as any progression at all. Sure, a choice between interchange designs may have an impact on signal progression, but we're probably talking about two nearly indistinguishable shades of crap, compared to Metro Detroit.
If someone's drowning, do you fuss over whether it's Lake Erie water or Evian that they are drowning in?
What are you arguing here? I would prefer to drive on a Boston corridor where 90% of the signals have crappy progression as opposed to a Boston corridor where 100% of the signals have crappy progression. The fact is any city could benefit from interchange designs that improve upon progression.
Quote from: jakeroot on April 06, 2015, 03:14:43 PM
Quote from: cl94 on April 06, 2015, 03:02:38 PM
Interchange design in much of the world is designed to get people onto the limited-access road as fast as possible, thus removing traffic from surface streets. This is the best design if arterials are clogged and the freeway has capacity, as you're minimizing traffic that backs up on the surface road.
But weren't freeways sort of designed as bypass roads? If you introduce too much local traffic onto them, you get congestion on the freeway.
I understand how people often use freeways, but to me, they should be used to go from A to C by bypassing B, not to go from A to B to C (in the former, you can still access C, but you must exit at an arterial and drive the extra distance).
Eh, not always. Take New York City's expressway system. Really was never meant to do anything than get cars off of the surface roads.
In some jurisdictions, the emphasis is on optimizing the performance of each intersection/interchange, not on having drivers hit a stream of green lights. This is especially true for areas that primarily use actuated signals rather than fixed timed ones. Many NYSDOT signals don't have a pre-programed timed sequence during ANY part of the day, not even rush hour.
Quote from: vdeane on April 06, 2015, 06:10:25 PM
In some jurisdictions, the emphasis is on optimizing the performance of each intersection/interchange, not on having drivers hit a stream of green lights. This is especially true for areas that primarily use actuated signals rather than fixed timed ones. Many NYSDOT signals don't have a pre-programed timed sequence during ANY part of the day, not even rush hour.
How about a preference for trucks exiting a rail yard, and entering an interstate?
The DDI here has simplified my commute immensely.
(https://www.aaroads.com/forum/proxy.php?request=http%3A%2F%2Ftapatalk.imageshack.com%2Fv2%2F15%2F04%2F06%2F18fc6662ba128e0ff26067991ea2e8ec.jpg&hash=4b199d34b6b3eca7821ceeed28d90c2babf84204)
Are the NYSDOT actuated signals mainly along rural high speed arterials where the signals are more spread out?
Signal progression is all well and good but interchanges often have concerns that are of more importance.
Of course, I live in a part of the country that just got their first SPUI two years ago and still thinks left exits are pretty neat, so I doubt signal progression is a realistic thing to hope for. OK-9 in Norman would be a great candidate for it, but no such luck.
Quote from: tradephoric on April 06, 2015, 08:23:13 PM
Are the NYSDOT actuated signals mainly along rural high speed arterials where the signals are more spread out?
Not necessarily. Near Buffalo, almost every NYSDOT signal is at least semi-actuated, including in dense parts of the suburbs. Traffic patterns are too erratic to do simple timing and the advanced demand-based systems are very costly. Only real exceptions are the few NYSDOT signals in downtown Buffalo, which are on green waves. Buffalo maintains most of the signals in the city, even along the few state-maintained roads (excluding Elm/Oak and Church, which are the aforementioned timed NYSDOT signals). There's a project going on to coordinate the signals along NY 78 and NY 324, but that's really it for state stuff. This holds true in most regions. NYC is synced, but
every signal in the City is city-maintained.
The I-270 example is pretty similar to how preference is assigned in most places. Might ruin any chance of progression, but it's very effective at getting trucks between the intermodal yard and the expressway.
Quote from: Scott5114 on April 06, 2015, 08:33:29 PM
Signal progression is all well and good but interchanges often have concerns that are of more importance.
This! I thought it was commonsense, but apparently not.
Quote from: kphoger on April 06, 2015, 11:55:26 PM
Quote from: Scott5114 on April 06, 2015, 08:33:29 PM
Signal progression is all well and good but interchanges often have concerns that are of more importance.
This! I thought it was commonsense, but apparently not.
Here is a comparison analysis of the diverging diamond interchange and partial cloverleaf interchanges:
http://fau.digital.flvc.org/islandora/object/fau%3A3779/datastream/OBJ/view/Comparative_analysis_between_the_diverging_diamond_interchange_and_partial_cloverleaf_interchange_using_microsimulation_modeling.pdf
The Parclo B4 had the shortest delay time and the fewest number of stops for all scenarios tested. In regards to max queue length, the Parclo B4 had the shortest queues in low volume scenarios but the highest queues in high volume scenarios. The explanation for the max queue length of the Parclo B4 is explained on page 92:
Quote
The maximum queue length on a ParClo B4 occurs at the off-ramps, where cars are trying to enter the crossroad, but are unable to do so since the crossroad is very congested and the vehicles wanting to go through the intersection do not have to stop since they have green throughout the whole cycle length. For the High volume flows, the DDI designs had a much better performance than the ParClo designs.The ParClo A4 had double the queue length than the DDIs, and the ParClo B4 had almost triple the maximum queue lengths at some instances compared to the DDIs.
It's incredibly important to note that the Parclo B4 being analyzed in this study had free-flowing loop ramps. If the off ramps were signalized the max queue of the Parclo B4 would likely be comparable to the other interchanges being analyzed.
The Parclo B4 outperformed the DDI and Parclo A4 in every MOE tested (besides max queue length at high volumes, which can be easily addressed with signalized off-ramps).
Quote from: tradephoric on April 06, 2015, 03:45:15 PM
Quote from: vtk on April 06, 2015, 02:54:52 PM
Quote from: tradephoric on April 06, 2015, 02:44:21 PM
Quote from: vtk on April 06, 2015, 01:46:13 PM
Made possible by the fact that Detroit's arterials are nearly all mile-grid roads with Michigan Lefts. How much of Boston or Atlanta would have to be demolished to make room for such a neat road system that is so agreeable to signal progression?
If signal progression is already bad, like in the case of Boston or Atlanta, wouldn't that be a good reason to choose interchange designs that improve upon progression? If someone is drowning would you try to hold their head under the water?
No, it doesn't work like that, and you missed my point. Unless you completely reconfigure the arterial network on a large scale in cities like that, the best signal progression that's even possible is still hardly recognizable as any progression at all. Sure, a choice between interchange designs may have an impact on signal progression, but we're probably talking about two nearly indistinguishable shades of crap, compared to Metro Detroit.
If someone's drowning, do you fuss over whether it's Lake Erie water or Evian that they are drowning in?
What are you arguing here? I would prefer to drive on a Boston corridor where 90% of the signals have crappy progression as opposed to a Boston corridor where 100% of the signals have crappy progression. The fact is any city could benefit from interchange designs that improve upon progression.
If a corridor doesn't already have good two-way signal progression, that's probably because the geometric configuration of the arterials doesn't support it. An "interchange design that improves upon progression" at one location along such a corridor isn't going to make any practical difference. You seem to think there's this additive effect, that every intersection independently contributes to the value of signal progression, but that's nonsense. There's no appreciable value until you have a run of a few arterial—arterial intersections, and then each additional intersection within the run adds more and more value. An interchange that doesn't ruin progression is no better than other interchanges if there's no progression to speak of. It doesn't create progression by itself.
Quote from: tradephoric on April 07, 2015, 01:01:29 AM
If the off ramps were signalized the max queue of the Parclo B4 would likely be comparable to the other interchanges being analyzed.
The Parclo B4 outperformed the DDI and Parclo A4 in every MOE tested (besides max queue length at high volumes, which can be easily addressed with signalized off-ramps).
Signalization of the off ramp would disrupt your through coordination, which seems to be your whole argument...
Quote from: johndoe on April 07, 2015, 07:54:56 AM
Signalization of the off ramp would disrupt your through coordination, which seems to be your whole argument...
Signalizing the off-ramps at a Parclo B4 wouldn't disrupt signal progression as the off-ramp signals would only stop one-direction of travel. Ever hear of a Restricted Crossing U-Turn intersection (RCUT)? A Parclo B4 is very similar to an RCUT operationally.
RCUT in Troy Michigan:(https://www.aaroads.com/forum/proxy.php?request=http%3A%2F%2Fi478.photobucket.com%2Falbums%2Frr144%2Ftradephoric%2FTransportation%2520Pictures%2FRandom%2FDallascomparison.jpg&hash=782c26ed28918b91f47019b216f5ad892ab9aa47)
Parclo B4 in Dallas, Texas:(https://www.aaroads.com/forum/proxy.php?request=http%3A%2F%2Fi478.photobucket.com%2Falbums%2Frr144%2Ftradephoric%2FTransportation%2520Pictures%2FRandom%2FDallasB4.jpg&hash=c626eea99f8ac9425ffba89bb3722f0c20dcb5c7)
One disadvantage of the RCUT is that traffic along the minor road wishing to turn left are not permitted to do so. They must first make a right at the major road and then make a U-turn. A Parclo B4 doesn't have this disadvantage as drivers coming off the freeway decide which off-ramp to take so that they are traveling in their desired direction.
In regards to safety, RCUTs have a proven safety record. Researchers from North Carolina State University have found that RCUTs reduce total accidents by 46% and reduce personal injury accidents by 63% when compared to conventional intersection designs. Parclo B4's should see similar reductions in injury accidents since the designs are near mirror images.
Quote from: vtk on April 07, 2015, 01:27:39 AM
If a corridor doesn't already have good two-way signal progression, that's probably because the geometric configuration of the arterials doesn't support it. An "interchange design that improves upon progression" at one location along such a corridor isn't going to make any practical difference. You seem to think there's this additive effect, that every intersection independently contributes to the value of signal progression, but that's nonsense. There's no appreciable value until you have a run of a few arterial—arterial intersections, and then each additional intersection within the run adds more and more value. An interchange that doesn't ruin progression is no better than other interchanges if there's no progression to speak of. It doesn't create progression by itself.
I think people have become apathetic to bad signal progression because it's so common. Some of the comments on this thread seem to be defending poor signal progression. If drivers get stopped at every other red light along a corridor, what's the big deal if they get stopped at a SPUI?
For Detroit drivers who routinely cruise long stretches without getting stuck at red lights, a progression killing interchange stands out like a sore thumb. It's annoying to cruise 10-miles down a corridor only to get stopped at a progression killing Parclo A4 interchange. The Parclo A4's are the most annoying to get stopped at since they have similar footprint/costs as a Parclo B4. If you are going to have a large footprint Parclo, pick the Parclo that maintains good signal progression! IMO, the Parclo B4 should be the preferred interchange design as opposed to the Parclo A4.
Quote from: tradephoric on April 07, 2015, 11:49:41 AMIf you are going to have a large footprint Parclo, pick the Parclo that maintains good signal progression! IMO, the Parclo B4 should be the preferred interchange design as opposed to the Parclo A4.
In Detroit. Almost everywhere else, your argument is weak at best. And I still assert an A4, SPUI, or DDI can potentially be engineered and operated so as not to completely kill progression in a Detroitoid arterial grid.
Tradephoric, can you show me what a signal that only stops one direction of traffic looks like in one of your time/distance diagrams? I want to try to get the visual language right.
Quote from: tradephoric on April 07, 2015, 11:49:41 AMSome of the comments on this thread seem to be defending poor signal progression. If drivers get stopped at every other red light along a corridor, what's the big deal if they get stopped at a SPUI?
That's not defending bad progression, but accepting it. Because if you don't have a neat grid or ROW wide enough for median U turns, good progression is basically impossible anyway. Due to left turn phases and clearance intervals, at each signal with another arterial you have less than a 50% chance of hitting the light on green, and a SPUI will be just another signal with the same chances. But a parclo B4 would only be slightly better on a corridor like this, with maybe better than 50% green probability (depending on the volume of traffic entering the freeway) and likely poor coordination with other signals if loop detectors are used. And if the exit ramps are also signalized to prevent weaving, then each direction of the surface corridor has two signals to deal with in the interchange, and the probability of getting through both of them on green may drop below 50%, so even if the metric is signal progression, the B4 is now comparable to a SPUI. And there are other things to consider while choosing an interchange design.
Quote from: vtk on April 07, 2015, 12:54:39 PM
Tradephoric, can you show me what a signal that only stops one direction of traffic looks like in one of your time/distance diagrams? I want to try to get the visual language right.
Here is an example of a Parclo B4 interchange near Miami, Florida with a corresponding time-distance diagram.
(https://www.aaroads.com/forum/proxy.php?request=http%3A%2F%2Fi478.photobucket.com%2Falbums%2Frr144%2Ftradephoric%2FTransportation%2520Pictures%2FRandom%2FB4aerial.jpg&hash=27152d2feb6eca2a2d3ac199ef91fe73bd41630d)
green circle icons = traffic signals that stop only one direction of travel
red circle icons = traffic signals that stop both directions of travel
(https://www.aaroads.com/forum/proxy.php?request=http%3A%2F%2Fi478.photobucket.com%2Falbums%2Frr144%2Ftradephoric%2FTransportation%2520Pictures%2FRandom%2FParcloB4time-distance.jpg&hash=0a674838bf1faeb4f4b0520d45d33dca3868355c)
Trade, I don't think any of us are saying signal timing isn't important. But at many service interchanges the through movement isn't the highest volume. Traffic signals are always going to delay someone...but if the through movement is half the volume of those turning left onto the freeway, why give the through movement priority at the expense of the majority of drivers?
The other thing we need to remember is the arrivals from the off-ramp. What if (assuming north is up in your picture) there are twice as many people going sb to eb as eb to nb? The green band at Dykes and 148th will be different. What if there is a huge development on one side of the interchange? Site conditions are going to vary, so it's not fair to say that just because the through movement doesn't get perfect "waves" the coordination isn't optimized.
Quote from: johndoe on April 07, 2015, 05:04:18 PM
Trade, I don't think any of us are saying signal timing isn't important. But at many service interchanges the through movement isn't the highest volume. Traffic signals are always going to delay someone...but if the through movement is half the volume of those turning left onto the freeway, why give the through movement priority at the expense of the majority of drivers?
You just have more options with a signal that only stops one direction. Assume the traffic volumes exiting one of the off-ramps during the PM rush is heavier than the thru traffic traveling on the arterial. Go ahead and time the heavier off-ramp to coordinate with the main signal. This will still only effect one direction of the corridor with a Parclo B4 (since the off-ramp signal being coordinated only stops one-direction). If you wanted to coordinate a heavy Parclo A4 off-ramp, you would be effecting both directions along the corridor. Closely spaced signals that stop both directions of travel leads to poor signal progression, regardless of what movement is being coordinated.
Quote from: johndoe on April 07, 2015, 05:04:18 PMwhy give the through movement priority at the expense of the majority of drivers?
So their eleven-light green streak doesn't get bummed, of course. It's just... such a downer!
Quote from: tradephoric on April 07, 2015, 01:35:34 PM
Quote from: vtk on April 07, 2015, 12:54:39 PM
Tradephoric, can you show me what a signal that only stops one direction of traffic looks like in one of your time/distance diagrams? I want to try to get the visual language right.
Here is an example of a Parclo B4 interchange near Miami, Florida with a corresponding time-distance diagram.
(https://www.aaroads.com/forum/proxy.php?request=http%3A%2F%2Fi478.photobucket.com%2Falbums%2Frr144%2Ftradephoric%2FTransportation%2520Pictures%2FRandom%2FB4aerial.jpg&hash=27152d2feb6eca2a2d3ac199ef91fe73bd41630d)
green circle icons = traffic signals that stop only one direction of travel
red circle icons = traffic signals that stop both directions of travel
(https://www.aaroads.com/forum/proxy.php?request=http%3A%2F%2Fi478.photobucket.com%2Falbums%2Frr144%2Ftradephoric%2FTransportation%2520Pictures%2FRandom%2FParcloB4time-distance.jpg&hash=0a674838bf1faeb4f4b0520d45d33dca3868355c)
Problem here tradephoric, is that you completely skipped a traffic light there. You missed the light between the intersections of Dykes Road/Sheridan Street and the I-75 SB onramp light.
http://goo.gl/maps/LusIa
Rickmastfan67, I was responding to VTK's request....
Quote from: vtk on April 07, 2015, 12:54:39 PM
Tradephoric, can you show me what a signal that only stops one direction of traffic looks like in one of your time/distance diagrams? I want to try to get the visual language right.
Included in the Parclo B4 time-distance are signals that stop both directions of traffic in addition to signals that stop only one direction of traffic. You should be critical of me for including Dykes Road and 148th Lane since VTK only asked for signals that stop just one-direction of traffic. For that, i apologize.
Quote from: kphoger on April 07, 2015, 11:17:31 PM
Quote from: johndoe on April 07, 2015, 05:04:18 PMwhy give the through movement priority at the expense of the majority of drivers?
So their eleven-light green streak doesn't get bummed, of course. It's just... such a downer!
Most drivers would appreciate cruising along a corridor without getting stopping at a red light. Your mocking and cavalier attitude towards good signal progression would not be appreciated by the general public. Why would you want to unnecessarily increase drivers delay and number of stops?
Some ideologues want to make driving such a living hell that people will either decide to move closer to work or take other modes of transportation. I'm not suggesting we build 10-lane roads everywhere, but the limited lane miles that are available should be efficient. For all i know maybe you bike to work everyday and don't care about signal progression, but a lot of people do. One may start to believe you're a wacked out ideologue based on some of your recent comments.
Maybe i am over zealot when it comes to designing corridors that achieve good signal progression. Of course, poll 1,000 drivers and ask them if they enjoy getting stopped at red lights.
Quote from: tradephoric on April 08, 2015, 11:01:12 AM
Quote from: kphoger on April 07, 2015, 11:17:31 PM
Quote from: johndoe on April 07, 2015, 05:04:18 PMwhy give the through movement priority at the expense of the majority of drivers?
So their eleven-light green streak doesn't get bummed, of course. It's just... such a downer!
Most drivers would appreciate cruising along a corridor without getting stopping at a red light. Your mocking and cavalier attitude towards good signal progression would not be appreciated by the general public. Why would you want to unnecessarily increase drivers delay and number of stops?
Some ideologues want to make driving such a living hell that people will either decide to move closer to work or take other modes of transportation. I'm not suggesting we build 10-lane roads everywhere, but the limited lane miles that are available should be efficient. For all i know maybe you bike to work everyday and don't care about signal progression, but a lot of people do. One may start to believe you're a wacked out ideologue based on some of your recent comments.
Maybe i am over zealot when it comes to designing corridors that achieve good signal progression. Of course, poll 1,000 drivers and ask them if they enjoy getting stopped at red lights.
It is extremely rare that an interchange ramp will produce more traffic than the cross street. But even then, you can't account for a green corridor for traffic coming off limited-access highways where in theory they could go on an endless loop without hitting a traffic light. If they go up the ramp and have the green, great. But if it's red, so be it. After that the lights can be timed to hit as many green lights as possible.
You can't achieve an infinity length of green lights. Even on the videos shown above, the corridors of green are shown for a certain point. The camera operator makes it a point to make a U-turn just before a red light.
Quote from: tradephoric on April 08, 2015, 11:01:12 AM
Maybe i am over zealot when it comes to designing corridors that achieve good signal progression.
You do seem just a bit more concerned with that one aspect of efficiency than the rest of us. But, please & by all means, redesign some corridors in Columbus with good two-way signal progression. Here are some that make the most sense as through corridors over significant distances:
- Cleveland Ave
- Hayden Run Rd, Bethel Rd
- Morse Rd
- Riverside Dr
- Fifth Ave
- Parsons Ave
- Frank Rd
- Refugee Rd
- Harrisburg Pk
- Broad St (particularly on the east side)
- Westerville Rd
- Powell Rd, Polaris Pkwy
I'm of the opinion that good two-way signal progression is essentially a lost cause on these corridors. Prove me wrong.
Quote from: vtk on April 08, 2015, 12:26:29 PM
Quote from: tradephoric on April 08, 2015, 11:01:12 AM
Maybe i am over zealot when it comes to designing corridors that achieve good signal progression.
You do seem just a bit more concerned with that one aspect of efficiency than the rest of us. But, please & by all means, redesign some corridors in Columbus with good two-way signal progression. Here are some that make the most sense as through corridors over significant distances:
- Cleveland Ave
- Hayden Run Rd, Bethel Rd
- Morse Rd
- Riverside Dr
- Fifth Ave
- Parsons Ave
- Frank Rd
- Refugee Rd
- Harrisburg Pk
- Broad St (particularly on the east side)
- Westerville Rd
- Powell Rd, Polaris Pkwy
I'm of the opinion that good two-way signal progression is essentially a lost cause on these corridors. Prove me wrong.
There are 22 signals along a 5-mile section of Broad St (from Nelson Road to Boe Bixby Road). All 22 signals stop both directions of traffic and the signals are irregularly spaced. This is what an optimized time-distance diagram looks like on Broad Street:
(https://www.aaroads.com/forum/proxy.php?request=http%3A%2F%2Fi478.photobucket.com%2Falbums%2Frr144%2Ftradephoric%2FTransportation%2520Pictures%2FRandom%2FAbroadTD_zps5ekal6cx.png&hash=97bdc49340d88e6b92b358e00a5e9ac0b46eb889)
There are 30 signals along a 5-mile section of Big Beaver Road (from Coolidge to Dequindre). Only 5 signals stop both directions of traffic and the signals are evenly spaced. This is what an optimized time-distance diagram looks like on Big Beaver:
(https://www.aaroads.com/forum/proxy.php?request=http%3A%2F%2Fi478.photobucket.com%2Falbums%2Frr144%2Ftradephoric%2FTransportation%2520Pictures%2FRandom%2FABigBTD_zps07stxecr.png&hash=cbf3a4fad9e9ddbe1e7fea3977bd3edd1fe915c1)
https://www.youtube.com/watch?v=eB2H4bGp4Jc
Moral of the story, if you want a corridor to achieve good signal progression reduce the number of signals that stop both directions of traffic. Traffic signals at DDIs, SPUIs, and Parclo A4s stop both direction of traffic, which is why they are so bad for progression.
Quote from: tradephoric on April 08, 2015, 11:01:12 AM
Quote from: kphoger on April 07, 2015, 11:17:31 PM
Quote from: johndoe on April 07, 2015, 05:04:18 PMwhy give the through movement priority at the expense of the majority of drivers?
So their eleven-light green streak doesn't get bummed, of course. It's just... such a downer!
Most drivers would appreciate cruising along a corridor without getting stopping at a red light. Your mocking and cavalier attitude towards good signal progression would not be appreciated by the general public. Why would you want to unnecessarily increase drivers delay and number of stops?
My point is that I remain unconvinced that stopping SOME drivers means the interchange as a WHOLE is unacceptable. It's ingrained in our psyche to think that, if a traffic control design negatively affects one movement of traffic (generally the movement we happen to be a part of), then the design must be inefficient. This is a nearsighted view of things. Your thesis may very well be correct, that DDIs and certain parclo variants may be less efficient than other designs, but I cannot accept mere interruption of signal progression along one of the corridors as the basis for that claim. It's only one piece of a puzzle, and not every puzzle even looks the same.
The bare fact of the matter is that ALL traffic control "increases drivers' delay" and all stoplights increase "number of stops". The key word, however, is "unnecessarily". Unnecessary for what? for whom? for what reasons?
Again, you're not looking at why a SPUI, DDI or A4s are getting put in places of conventional interchanges: They're not for the through traffic on the crossroad. They're there to get traffic off and on the highway the crossroad's interchanging with. Yes, there will be through traffic going through a DDI/SPUI/A4; yes they will be delayed by less than 'optimal' signal timing because of these interchanges, but they're not the target of the interchange.
Furthermore, it is impossible to provide free-flow traffic signal progression on a two-way corridor. The direction that enjoys free-flow will result in poor timing in the other direction. Only one-way grids can avoid that, and even then it doesn't always work.
Quote from: Bickendan on April 08, 2015, 03:28:05 PM
Furthermore, it is impossible to provide free-flow traffic signal progression on a two-way corridor. The direction that enjoys free-flow will result in poor timing in the other direction. Only one-way grids can avoid that, and even then it doesn't always work.
Let me know if you don't understand how to read a time-distance diagram. The dash cam video demonstrates good two-way progression along a two-way corridor.
(https://www.aaroads.com/forum/proxy.php?request=http%3A%2F%2Fi478.photobucket.com%2Falbums%2Frr144%2Ftradephoric%2FTransportation%2520Pictures%2FRandom%2FABigBTD_zps07stxecr.png&hash=cbf3a4fad9e9ddbe1e7fea3977bd3edd1fe915c1)
https://www.youtube.com/watch?v=eB2H4bGp4Jc
Quote from: tradephoric on April 08, 2015, 02:59:01 PM
There are 22 signals along a 5-mile section of Broad St (from Nelson Road to Boe Bixby Road). All 22 signals stop both directions of traffic and the signals are irregularly spaced. This is what an optimized time-distance diagram looks like on Broad Street:
(https://www.aaroads.com/forum/proxy.php?request=http%3A%2F%2Fi478.photobucket.com%2Falbums%2Frr144%2Ftradephoric%2FTransportation%2520Pictures%2FRandom%2FAbroadTD_zps5ekal6cx.png&hash=97bdc49340d88e6b92b358e00a5e9ac0b46eb889)
Can it get any better than that on Broad St? What if some of the signals were changed so they don't stop both directions of traffic at the same time? There's no room for median U-turns so left turns have to be accommodated somehow; I'm thinking lead/lag operation, for example the following phase sequence: cross traffic left turns, cross traffic thru, eastbound thru + left, eastbound & westbound, westbound thru+left. The signals at minor streets can be set up that way (or with eastbound & westbound reversed) to try to work around the waves of traffic set up between the more significant intersections, which will probably have eastbound and westbound stopped at the same time, and let's be honest, a greater proportion of red time because there's more cross traffic. Anyway, does it get much better using that approach?
Here is Broad St with lead/lag optimization. It's a bit disjointed but lead/lag will definitely help with progression. Some signals will lead, some will lag, and some will lead/lag based on what SYNCHRO calculates to be the lowest delay.
(https://www.aaroads.com/forum/proxy.php?request=http%3A%2F%2Fi478.photobucket.com%2Falbums%2Frr144%2Ftradephoric%2FTransportation%2520Pictures%2FRandom%2FAbroadleadlag_zps1o9wiuwf.png&hash=81182f030b7eebed8631886ed32a4c4678630559)
Quote from: tradephoric on April 08, 2015, 05:49:25 PM
Here is Broad St with lead/lag optimization. It's a bet disjointed but lead/lag will definitely help with progression. Some signals will lead, some will lag, and some will lead/lag based on what SYNCHRO calculates to be the lowest delay.
(https://www.aaroads.com/forum/proxy.php?request=http%3A%2F%2Fi478.photobucket.com%2Falbums%2Frr144%2Ftradephoric%2FTransportation%2520Pictures%2FRandom%2FAbroadleadlag_zps1o9wiuwf.png&hash=81182f030b7eebed8631886ed32a4c4678630559)
Hey that's a lot better than I expected, though the eastbound wave gets collectively screwed at Cassady through Roosevelt and the westbound wave gets collectively screwed at Napoleon through James and potentially again at Drexel. And Columbus drivers aren't used to so many lagging left operations (most typical is leading left for both directions, which doesn't appear to be the case at any signals in your diagram). If the corridor runs this well, then signal progression is indeed a valid (if not overriding) concern in choosing an interchange design. However, the other half of my argument is that the Parclo B4 is not the only design that can be friendly to signal progression. I'll be posting more on that shortly.
Imagine an idealized Detroitoid grid of arterials spaced one mile apart, with Michigan lefts. With signal periods of 144s, traffic can cruise along at 50 MPH indefinitely. It's ideal two-way progression. A place like this stands to lose the most from poor interchange design, at least in the context of signal progression.
Now let's throw in some interchanges that aren't parclo B4s.
Parclo A4
(https://www.aaroads.com/forum/proxy.php?request=http%3A%2F%2Fvidthekid.info%2Fimghost%2Fdetroitoid-a4.png8.png&hash=71cc16b743cf9cbf3b48f69677c46b7d43f9e0b4)
This interchange has a "wide stance", that is, its exit ramp termini are quite far (3168ft) apart. The signals at this interchange don't interrupt the green waves on the arterial at all. The green time for the exit ramps is nearly 40 seconds (actually about 43s if you also count the yellow) out of the 144s cycle, which should be plenty if there exiting traffic is small compared to the arterial through traffic.
SPUI
(https://www.aaroads.com/forum/proxy.php?request=http%3A%2F%2Fvidthekid.info%2Fimghost%2Fdetroitoid-spui.png8.png&hash=eea938916907d045cbc16278c85fbd8abd5e77db)
This one requires the freeway to be a bit off-center in the mile-grid. The signal operates in a lead-lag manner: westbound thru + left onto the freeway (plus northbound exit right to eastbound), eastbound & westbound thru, eastbound thru + left onto the freeway (plus southbound exit right to westbound), then left turns off of the freeway ramps. In the timing configuration shown, the thru green waves on the arterial aren't interrupted at all; left turns onto the freeway and right turns off the freeway get nearly 40 seconds of green; left turns off the freeway get nearly 30 seconds of green. The timing can be tweaked to allow more time for turning movements, at some expense to the thru green waves on the arterial.
Diverging Diamond
Example 1
(https://www.aaroads.com/forum/proxy.php?request=http%3A%2F%2Fvidthekid.info%2Fimghost%2Fdetroitoid-ddi1.png8.png&hash=244288bfcc7fc11f25314c48d78401999eda5ab4)
The freeway is back to the middle of the mile again. This example is designed to preserve the thru green waves, but about 20% of the wave gets delayed for a few seconds at the DDI. Traffic turning off the freeway potentially gets delayed for a whole signal cycle between the DDI itself and the first major intersection on the surface arterial. Traffic turning onto the freeway experiences no delay.
Example 2
(https://www.aaroads.com/forum/proxy.php?request=http%3A%2F%2Fvidthekid.info%2Fimghost%2Fdetroitoid-ddi2.png8.png&hash=d289781805ef9953ffc6b6ceabf8cfadc9dfd278)
Another way to time the DDI that is less focused on the thru arterial traffic, because DDIs are usually chosen when the exiting and entering traffic is significantly greater than the thru traffic staying on the surface arterial. Here I've also shown cars that just exited the freeway as blue lines, and the lines turn red where they represent queuing vehicles. Only about 40% of the thru green wave gets by unscathed, and it's probably less than that due to delays due to slowing down for the DDI's unconventional geometry. Traffic turning right onto the freeway still experiences no delay, and traffic turning left onto the freeway experiences the same amount of delay as thru traffic. Traffic exiting the freeway has slightly reduced delay compared to Example 1, and has a slightly increased chance of transitioning to the arterial with no delay at all at the DDI or at subsequent intersections. To be honest, this doesn't really look that much better than my first DDI example; maybe I could come up with a better timing if I tried again, but I don't really feel like it. I'm willing to call Example 1 "good enough".
This may be a silly question, but I used to drive in and around the Western Detroit area, and knew even when I was a kid that setting the cruise at 45 MPH could get you past miles of green lights, on the majority of North-South and East-West surface streets. But when it came to the "spoke" roads which came out of Downtown Detroit (Michigan, Woodward, Gratiot, Grand River,...) and were not true N-S/E-W roads, which of the two roads (grid vs. spoke) had the green light advantage?
You didn't see it as much on the west side since it was only Grand River and Michigan Avenues that would be the sore thumbs that could throw off the flow, and I mostly cruised Telegraph and the other grid roads.
BTW, Toledo had a pretty decent signal system with many of their major intersections on a lead/lag cycle for opposing traffic. Though not a true Detroit flow due to some oddball streets and improper spacing of traffic lights, it did help in many cases and the lights at some of the major intersections were programmed to flip the direction of the lead/lag depending on the AM or PM rush hour.
Quote from: thenetwork on April 09, 2015, 10:26:12 AM
This may be a silly question, but I used to drive in and around the Western Detroit area, and knew even when I was a kid that setting the cruise at 45 MPH could get you past miles of green lights, on the majority of North-South and East-West surface streets. But when it came to the "spoke" roads which came out of Downtown Detroit (Michigan, Woodward, Gratiot, Grand River,...) and were not true N-S/E-W roads, which of the two roads (grid vs. spoke) had the green light advantage?
The signals are evenly spaced along the spoke roads in Detroit which is key to achieve good two-way signal progression. The signals are much closer though (0.6 miles as opposed to 1.0 miles) so a shorter cycle is needed to achieve good dual progression. Instead of 144 second cycles along the mile roads, the diagonal spoke roads will run roughly 90 second cycles to achieve dual progression (assuming 50 mph). So the mile roads might run a 70 second low cycle at night and a 140 second high cycle during the rushes to achieve dual. On the other hand, a spoke road will run a 90 second cycle length 24/7. Both setups are capable of achieving good dual and I'd just say each setup has its own set of pros and cons.
(https://www.aaroads.com/forum/proxy.php?request=http%3A%2F%2Fi478.photobucket.com%2Falbums%2Frr144%2Ftradephoric%2FTransportation%2520Pictures%2FRandom%2FWW-time_zpsoqvzmkyf.png&hash=e9a705dee6bf3329b7001b9bd0e7414adc65d109)
I like those time-distance diagrams you came up with VTK. The Parclo B4 solves the progression problem but probably isn't very practical because of the amount of space it would take up. The lead/lag SPUI is most interesting, but it requires the interchange to be offset to maximize the effects of lead/lag optimization. In regards to the DDI example, I wonder if a 50 mph speed limit could be safely maintained at the crossing conflict points. If the speed limit along a 50 mph corridor was reduced to 35 mph surrounding the DDI, progression would probably suffer. What is a typical speed limit surrounding a DDI interchange?
I must say I am quite impressed with what you showed in that SPUI example and I see no reason why lead/lag SPUIs couldn't work. Does anyone know if any lead/lag SPUIs currently exist?
Quote from: tradephoric on April 09, 2015, 02:01:30 PM
Does anyone know if any lead/lag SPUIs currently exist?
http://books.google.com/books?id=t0jfX9fK5oUC&pg=PA19
I can't find which one it is.
Quote from: kphoger link=topic=15118.msg2056514#msg2056514
My point is that I remain unconvinced that stopping SOME drivers means the interchange as a WHOLE is unacceptable. It's ingrained in our psyche to think that, if a traffic control design negatively affects one movement of traffic (generally the movement we happen to be a part of), then the design must be inefficient. This is a nearsighted view of things. Your thesis may very well be correct, that DDIs and certain parclo variants may be less efficient than other designs, but I cannot accept mere interruption of signal progression along one of the corridors as the basis for that claim. It's only one piece of a puzzle, and not every puzzle even looks the same.
In a recent study, the Parclo B4 had the lowest delay and fewest number of stops when compared to the DDI and Parclo A4:
QuoteCOMPARATIVE ANALYSIS BETWEEN THE DIVERGING DIAMOND INTERCHANGE AND PARTIAL CLOVERLEAF INTERCHANGE USING MICRO SIMULATION MODELING
http://fau.digital.flvc.org/islandora/object/fau%3A3779/datastream/OBJ/view/Comparative_analysis_between_the_diverging_diamond_interchange_and_partial_cloverleaf_interchange_using_microsimulation_modeling.pdf
Two simple reasons why the Parclo B4 minimizes delays:
#1. Parclo B4 on/off ramp signals only stops one direction of traffic making good signal progression possible. This reduced delay for drivers on the corridor. With DDIs, SPUIs, and Parclo A4s, traffic signals stop both directions of travel killing good signal progression and increasing delays.
#2. Drivers exiting the freeway at a Parclo B4 make a simple right turn to enter onto the arterial. Drivers exiting the freeway just keep moving if there are gaps in traffic along the arterial. This reduces delay for drivers exiting the freeway. With DDIs, SPUIs, and Parclo A4s, drivers exiting the freeway making a left onto the arterial must wait for a green light before proceeding increasing delays. How annoying is it to wait at a red light at 2AM when no traffic is coming? That scenario happens routinely for drivers exiting the freeway at DDIs, SPUIs, and Parclo A4s.
Quote from: tradephoric on April 09, 2015, 02:01:30 PM
Does anyone know if any lead/lag SPUIs currently exist?
Plumb Lane & US 395/I-580 in Reno, NV. It is lead-lag due in part to geometry--a former tight diamond converted to modified SPUI (with partial frontage roads) without reconstructing the existing freeway. Left turns can't quite proceed together in a couple directions, and it is an unusually wide SPUI intersection that takes some getting used to. It is helpful in this case that Plumb Lane ends just east of here at the Reno airport entrance, so through progression is not a factor.
I feel like some of the SPUIs in the Las Vegas area may run lead/lag turns. I can't think of any specific examples, but feel I have seen such operation before. Vegas' coordination system extensively utilizes lead/lag phasing in order to maximize two-way through progression on major arterials, so it stands to reason that lead/lag would be used at the SPUI signals as well.
Quote from: tradephoric on April 13, 2015, 12:29:53 AM
How annoying is it to wait at a red light at 2AM when no traffic is coming? That scenario happens routinely for drivers exiting the freeway at DDIs, SPUIs, and Parclo A4s.
That scenario exists for drivers approaching nearly every traffic light everywhere; more so for those not on the main thru street.
Quote from: jeffandnicole on April 13, 2015, 08:21:08 AM
Quote from: tradephoric on April 13, 2015, 12:29:53 AM
How annoying is it to wait at a red light at 2AM when no traffic is coming? That scenario happens routinely for drivers exiting the freeway at DDIs, SPUIs, and Parclo A4s.
That scenario exists for drivers approaching nearly every traffic light everywhere; more so for those not on the main thru street.
The scenario doesn't exist for drivers exiting the freeway at a Parclo B4. All drivers exiting the freeway at a Parclo B4 make a simple right turn onto the arterial and experience minimal delays. There are other advantages to the Parclo B4 interchange, specifically maintaining good signal progression along the corridor (which also helps reduce delays).
MDOT is in the process of redesigning a full cloverleaf interchange at I-75 & Holland Road near Saginaw. Here's a link to the project report:
https://www.michigan.gov/documents/mdot/MDOT_I-75_Widening_in_Saginaw_County_Environmental_Assessment_422371_7.pdf
Here are models of the interchange running 2035 peak hour volumes as a Parclo B4 and a Parclo AB4 (MDOT's preferred alternative). Which interchange design has the lowest delay?
https://www.youtube.com/watch?v=9y-8okb2VOA
https://www.youtube.com/watch?v=7C_1qd34e4Y
Quote from: tradephoric on April 13, 2015, 10:01:13 AM
Quote from: jeffandnicole on April 13, 2015, 08:21:08 AM
Quote from: tradephoric on April 13, 2015, 12:29:53 AM
How annoying is it to wait at a red light at 2AM when no traffic is coming? That scenario happens routinely for drivers exiting the freeway at DDIs, SPUIs, and Parclo A4s.
That scenario exists for drivers approaching nearly every traffic light everywhere; more so for those not on the main thru street.
The scenario doesn't exist for drivers exiting the freeway at a Parclo B4. All drivers exiting the freeway at a Parclo B4 make a simple right turn onto the arterial and experience minimal delays. There are other advantages to the Parclo B4 interchange, specifically maintaining good signal progression along the corridor (which also helps reduce delays).
If it exists in the first place.
Besides, there are a host of things to look when engineering an intersection. You're in bed with the B4, but a real engineer is going to look at a whole lot of scenarios to determine if it's the best option.
Quote from: jeffandnicole on April 13, 2015, 11:25:16 AM
Quote from: tradephoric on April 13, 2015, 10:01:13 AM
Quote from: jeffandnicole on April 13, 2015, 08:21:08 AM
Quote from: tradephoric on April 13, 2015, 12:29:53 AM
How annoying is it to wait at a red light at 2AM when no traffic is coming? That scenario happens routinely for drivers exiting the freeway at DDIs, SPUIs, and Parclo A4s.
That scenario exists for drivers approaching nearly every traffic light everywhere; more so for those not on the main thru street.
The scenario doesn't exist for drivers exiting the freeway at a Parclo B4. All drivers exiting the freeway at a Parclo B4 make a simple right turn onto the arterial and experience minimal delays. There are other advantages to the Parclo B4 interchange, specifically maintaining good signal progression along the corridor (which also helps reduce delays).
If it exists in the first place.
Besides, there are a host of things to look when engineering an intersection. You're in bed with the B4, but a real engineer is going to look at a whole lot of scenarios to determine if it's the best option.
I'm in bed with interchange designs that minimizes total network driver delay. In the specific example of I-75 & Holland Road, the Parclo B4 appears to achieve that. You might be in bed with inefficient, red light stopping designs like SPUIs and DDIs. No thank you.
I'm in bed with sheep.
Quote from: jeffandnicole link=topic=15118.msg2057678#msg2057678
You're in bed with the B4, but a real engineer is going to look at a whole lot of scenarios to determine if it's the best option.
The microsimulation study found that the Parclo B4 resulted in lower delays and fewer stops when compared to Parclo A4s and DDIs (when tested under a variety of conditions). I posted SYNCHRO models at I-75 & Holland Road with 2035 peak hour volumes, to visualize the Parclo B4 interchange with MDOT's preferred alternative. I don't see traffic breaking down in the Parclo B4 model. What am I missing? All you can come back with is "a real engineer is going to look at a whole lot of scenarios to determine if it's the best option" . Now that is profound.
Convince me why the Parclo B4 isn't superior to MDOT's preferred alternative.
https://www.youtube.com/watch?v=9y-8okb2VOA
https://www.youtube.com/watch?v=7C_1qd34e4Y
I take it vehicles are also going 65 mph on the ramps, based on the videos you are showing us.
And these videos are showing very low-level traffic volumes. I don't see any congestion in either scenario. Present to us rush hour traffic scenarios, not 10am "it's after rush hour but before people start going out and shop" scenarios.
Also, how is traffic affected down the roads? The videos are showing the effects of traffic in the interchange only, not on a broader scale.
The point remains:
Signal progression is only a key factor when a significant portion of the surface street traffic is through traffic.
Scenarios in which DDIs are supposed to be considered are those in which a significant portion of the surface street traffic is turning onto the expressway. At least in theory, were talking about apples and oranges.
Are DDIs only chosen for locations that meet the criteria it was designed for? No. Perhaps that is where the breakdown is. So let's turn the table: Can you envision a scenario in which the amount of left-turning surface-to-expressway traffic is so great that the DDI ends up outperforming the B4 due to the former's free-flowing ramps?
Quote from: jeffandnicole on April 13, 2015, 02:50:23 PM
I take it vehicles are also going 65 mph on the ramps, based on the videos you are showing us.
I'm sure you could find more than just the speed of the ramps being off if you looked closely. If I was a consultant getting paid $1.4 million dollars for a traffic study these models would look perfect and the results probably wouldn't differ by much (the Parclo B4 would still be displaying smooth traffic flow with minor delays).
Quote from: jeffandnicole on April 13, 2015, 02:50:23 PM
And these videos are showing very low-level traffic volumes. I don't see any congestion in either scenario. Present to us rush hour traffic scenarios, not 10am "it's after rush hour but before people start going out and shop" scenarios.
The models were based on 2035 peak hour volumes. I used the peak volumes detailed in the MDOT report.
Quote from: jeffandnicole on April 13, 2015, 02:50:23 PM
Also, how is traffic affected down the roads? The videos are showing the effects of traffic in the interchange only, not on a broader scale.
The green bands for each model should give you a good idea how the adjacent signals interact with the interchange signals. Parclo B4 leads to smooth signal progression with much larger green bands compared to the Parclo AB4 (MDOT's preferred alternative).
MDOT preferred alternative:(https://www.aaroads.com/forum/proxy.php?request=http%3A%2F%2Fi478.photobucket.com%2Falbums%2Frr144%2Ftradephoric%2FTransportation%2520Pictures%2FRandom%2FMDOTgreenband_zpsgerufx1j.png&hash=b67ba39abdc732ac1d1eac6a0466747f9bb954c8)
Parclo B4:(https://www.aaroads.com/forum/proxy.php?request=http%3A%2F%2Fi478.photobucket.com%2Falbums%2Frr144%2Ftradephoric%2FTransportation%2520Pictures%2FRandom%2FPB4GreenBand_zpsaumuadg3.png&hash=7909fdecc67ca27c4d8cd2845d31298f46493802)
Quote from: kphoger on April 13, 2015, 02:55:16 PM
So let's turn the table: Can you envision a scenario in which the amount of left-turning surface-to-expressway traffic is so great that the DDI ends up outperforming the B4 due to the former's free-flowing ramps?
Left-turning surface-to-expressway traffic at a DDI still must cross opposing lanes of traffic before entering the freeway... they just do so at a signal upstream of the free-flowing on-ramp. I don't see why a DDI would outperform a B4, even if the left-turning surface-to-expressway traffic is high. They have diverging diamonds models in SYNCHRO and it might be interesting to compare SYNCHRO models of DDIs and Parclo B4s with various traffic volume scenarios.
If left-turning traffic onto the freeway is the heaviest movement, then consider a folded interchange (which is basically a B4/DDI hybrid). Unlike the DDI which diverge all traffic on the surface street, the folded interchange only diverge traffic that actually will be entering onto the freeway.
http://sabra-wang.com/media/TheFoldedInterchangeAnUnconventionalDesignfortheReconstructionofCloverleafInterchangesKeithRiniker.pdf
https://www.youtube.com/watch?v=ZZZOBPyHuCM
The I-695 at US 40 folded interchange study (linked in the previous post) looked at the average delay per vehicle for a number of different interchange alternatives. The existing Parclo B4 had 15 second average delay per vehicle compared to roughly 75 second for the DDI.
(https://www.aaroads.com/forum/proxy.php?request=http%3A%2F%2Fi478.photobucket.com%2Falbums%2Frr144%2Ftradephoric%2FTransportation%2520Pictures%2FRandom%2FLOS_zps40v02ztw.png&hash=7be851b8168dcfcef390abf7654735809a7e6491)
Quote from: kphoger on April 13, 2015, 02:55:16 PM
Scenarios in which DDIs are supposed to be considered are those in which a significant portion of the surface street traffic is turning onto the expressway. At least in theory, were talking about apples and oranges.
The DDI at Bangerter Hwy and Utah State 201 is a good example of a DDI that probably should never have been constructed. Bangerter Hwy is a major 6-lane boulevard that does get a lot of through traffic....it's the Telegraph Road of Salt Late City. Here is my feeble attempt at modeling the DDI on SYNCHRO:
https://www.youtube.com/watch?v=LsHEy461w3o
Here is the same DDI in action. Thru drivers on Bangerter Hwy who get a green at Camera 1 come straight to a red light at Camera 2. This bad progression continues throughout the entire video. The beginning of the platoon on Bangerter Hwy is being led straight into the dilemma zone! The DDI is often described as an innovative interchange... that's effed up innovation.
https://www.youtube.com/watch?v=RhazZu4xMeA
This topic has sort of gone a million ways, here are a few thoughts:
-the paper posted earlier doesn't have any volume scenarios where turns from the cross street are greater than through volumes
-the "folded interchange " might be great in some situations, one drawback is that it requires more bridge area
I feel like a broken record, but assuming the same geometry is either always good or always bad is foolish. Each interchange is unique in both traffic and project goals.
I'm not totally opposed to DDIs. Here is a scenario where a DDI works well...
https://maps.google.com/maps?ll=39.156138,-76.74507&spn=0.003428,0.003406&t=h&z=18
The one thing i don't like about this design is that drivers can't make a simple right on red when exiting the freeway. Again, just adding delay. If the sight distance at DDIs is such that you can't allow a driver exiting the freeway to make a simple right on red, that's just one more reason not to like DDIs.
https://maps.google.com/maps?ll=39.15584,-76.74326&z=19&t=h&output=classic&dg=brw
Quote from: tradephoric on April 14, 2015, 02:07:04 PM
I'm not totally opposed to DDIs. Here is a scenario where a DDI works well...
I want to know what was wrong with the roundabouts that were there before.
OT: How often are modern roundabouts removed and replaced with signalized junctions?
Quote from: tradephoric on April 14, 2015, 02:07:04 PM
The one thing i don't like about this design is that drivers can't make a simple right on red when exiting the freeway. Again, just adding delay. If the sight distance at DDIs is such that you can't allow a driver exiting the freeway to make a simple right on red, that's just one more reason not to like DDIs.
I suspect it's to make sure that drivers don't accidentally look at the wrong traffic (since they need to look to the far side of the road rather than the near one, and drivers not from the area may not know to do that) and get T boned.
Quote from: vdeane on April 14, 2015, 03:22:04 PM
Quote from: tradephoric on April 14, 2015, 02:07:04 PM
The one thing i don't like about this design is that drivers can't make a simple right on red when exiting the freeway. Again, just adding delay. If the sight distance at DDIs is such that you can't allow a driver exiting the freeway to make a simple right on red, that's just one more reason not to like DDIs.
I suspect it's to make sure that drivers don't accidentally look at the wrong traffic (since they need to look to the far side of the road rather than the near one, and drivers not from the area may not know to do that) and get T boned.
That's a legitimate reason to have a "˜no right turn on red' sign at that DDI, but it's still annoying getting stuck at a red light at 2AM waiting to make a right turn. There are other interchange designs that would allow a simple right turn on red... *cough, cough* the Parclo B4.
Quote from: jakeroot on April 14, 2015, 02:59:16 PM
OT: How often are modern roundabouts removed and replaced with signalized junctions?
Not often enough! :bigass:
Quote from: hbelkins on April 15, 2015, 11:16:53 AM
Quote from: jakeroot on April 14, 2015, 02:59:16 PM
OT: How often are modern roundabouts removed and replaced with signalized junctions?
Not often enough! :bigass:
(https://www.aaroads.com/forum/proxy.php?request=http%3A%2F%2Fi.imgur.com%2Foov56.gif&hash=46d2b4e87f856af9ecf24c5d1b51f08d6de416fa)
An advantage of signalizing the Parclo B4 off-ramps is that acceleration/deceleration lanes aren't needed. In the examples below, the Parclo B4 only has to accommodate 4-lanes of traffic over the bridge deck as opposed to 6 with the DDI (since there are no accel/decl lanes). The Parclo B4 maintains good signal progression and all traffic exiting the freeway are allowed to make a simple right turn on red. The DDI you get bad signal progression and drivers exiting the freeway experience delay (exiting freeway drivers making a left must wait for a green light, exiting freeway drivers making a right could potentially see a "no turn on red" sign as previously discussed).
DDI = Drivers Delayed Indefinitely
https://youtu.be/yU3B9kRBSLI
https://youtu.be/NQVlEchM3ck
Quote from: tradephoric on April 16, 2015, 03:07:30 PM
DDI = Drivers Delayed Indefinitely
Your zeal exceeds the substance of your arguments.
Quote from: vtk on April 16, 2015, 05:45:31 PM
Quote from: tradephoric on April 16, 2015, 03:07:30 PM
DDI = Drivers Delayed Indefinitely
Your zeal exceeds the substance of your arguments.
"Drivers Delayed Indefinitely" is still less dramatic than "Death Diamond Interchange".
Quote from: tradephoric on April 16, 2015, 06:24:42 PM
Quote from: vtk on April 16, 2015, 05:45:31 PM
Quote from: tradephoric on April 16, 2015, 03:07:30 PM
DDI = Drivers Delayed Indefinitely
Your zeal exceeds the substance of your arguments.
"Drivers Delayed Indefinitely" is still less dramatic than "Death Diamond Interchange".
'A haiku on the subject of the Diverging Diamond'
A Parclo 4B
What an interchange for me
Holy cow, 4B
Are drivers exiting the freeway making a left onto the arterial allowed to make a "˜left-turn on red' at a DDI? If not, why not? Drivers are being needlessly delayed when they are not allowed to merge into gaps along the arterial. This video is the best argument against the DDI. Drivers along a major 6-lane arterial get a green light only to come straight to a red at a signal 800 feet away. This bad progression continues throughout the entire video. How anybody could be impressed with the operation of this DDI is beyond me.
https://www.youtube.com/watch?v=RhazZu4xMeA#t=19
Quote from: tradephoric on April 17, 2015, 10:11:37 AM
Are drivers exiting the freeway making a left onto the arterial allowed to make a "˜left-turn on red' at a DDI? ... Drivers along a major 6-lane arterial get a green light only to come straight to a red at a signal 800 feet away.
Left turn on red? In Ohio, yes, unless there's a sign prohibiting it.
As for your six lane arterial, the only traffic from the artierial that will hit both lights at a DDI is the through traffic. Usually, through surface traffic is not the main concern at a DDI. If there's a lot of traffic on this six lane arterial that is not getting on the freeway one way or another, then I agree a DDI was a poor choice
for this specific location. This reasoning does not extend to condemn all DDIs.
Here is a great place where I think a DDI would work. Canyon Road @ WA-512, south of Seattle. Canyon Road is a major arterial, really throughout its length, but definitely moreso from the interchange below and to the right (south in real-life, up is east). From the image, you can tell from just the width of the arterial that Canyon Road is a lot busier on one side of the interchange, thus most of the traffic at the interchange is turning traffic; you can see from the image the cat-tracks of vehicles and the major movements. Canyon road spans up to 8 lanes south of the interchange pictured, but north, it drops to two (just past the next intersection). Coming from the left side of the image (approaching from the north), traffic backs up for a few blocks because of the incredibly long phase for both the off-ramp and the left turn onto the onramp. Because these are the major movements, the through signal is very short. There isn't a lot of traffic coming from the north, but it backs up so much because of the short signal phase.
FWIW, Canyon Road filters commuter traffic in both directions, morning and night. There's a large industrial park south of the interchange in Frederickson (namely, Boeing, and the factory that builds the walls for the Alaskan Way Tunnel) that both employ thousands of workers. Thus, there's really no dominant movement at any point during the day.
Also, because of the large industrial nature of the areas south of the interchange, there's a lot of trucks coming through this interchange (just look at the satellite shot), many of which are incredibly long, carrying airplane fuselages. So, especially taking into account the interchange geography (tight land use on both sides) and the fact that many large trucks use the interchange, I'm not sure a loop ramp would work here.
http://goo.gl/8KcZlI
(https://www.aaroads.com/forum/proxy.php?request=http%3A%2F%2Fi.imgur.com%2FoaQojD9.png&hash=5284d06cb6435077ebdc82ebc70bd9e07d4f5f9f)
Here's another DDI along a heavily traveled corridor (Pleasant Hill Road in Atlanta).
https://maps.google.com/maps?ll=33.952249,-84.129961&spn=0.001462,0.001725&t=h&z=19
This DDI replaced a tight diamond interchange. The space limitations at this interchange limited what interchange design could be selected (a Parclo B4 was obviously out of the question... the loop ramps wouldn't fit). An argument can be made that a DDI is more efficient than a tight diamond. However, is it a huge success to replace an inefficient tight diamond interchange with a slightly less inefficient DDI? Each design stops both directions of travel along the corridor, leading to excess driver delays due to poor signal progression. The DDI is only arguably better than the tight diamond it replaced.
It's not always practical to convert a tight diamond to a Parclo B4 (Jake just gave another perfect example). However, when the space is available shouldn't the Parclo B4 be the preferred interchange alternative? MDOT was considering replacing the full cloverleaf interchange at I-75 & Holland Road with a DDI, but there was enough public resistance that they scrapped the plans. I just don't understand the fascination with the DDI to where you see full cloverleafs (that have the space for efficient Parclo B4s) are being converted to inefficient DDIs.
I keep pushing the Parclo B4 because it's one of the few interchange designs where the on/off ramp signals only stop one directions of travel along the corridor. That's huge for reducing driver delay.
ODOT doesn't like Parclo B interchanges. I think, more specifically, they don't like loop exit ramps, because apparently some drivers don't decelerate early enough and lose control on the loop. This disfavor has only existed for about the last 10 years or so.
Quote from: tradephoric on April 17, 2015, 03:51:58 PM
[A DDI] stops both directions of travel along the corridor
You keep saying that, but it's not really true. Each signal at a DDI stops one direction or the other – not both directions – at any given time. Taken together, there almost certainly is some time when neither direction can go through both signals, but in the cases where DDIs are usually chosen, it is decided that this doesn't really matter.
A DDI is usually built where most of the surface road traffic approaching the interchange gets on the freeway, and most of the surface road traffic leaving the interchange has just exited the freeway. Therefore, it is of little use to talk about signal progression along "the corridor" because, essentially, you have two distinct surface road corridors that end at that interchange.
Would I be wrong if I say a typical sample of traffic approaching a DDI on a surface road is about 40% entering the freeway to the right, 40% entering the freeway left, and 20% continuing on the surface road? Since nobody can answer before I continue typing the post, I'm going to go with those numbers for an example. I think they're good numbers for a hypothetical DDI.
So you've got this arterial boulevard with a big pack of cars coming towards it, which has ridden a green wave for miles. Great. They hit the DDI, and 40% of the cars immediately turn right to enter the freeway. No delay for them. The other 60% gets to the first traffic light. Now if I'm setting up the timing for this DDI, I'd probably have it set so this first light is green a little less than half the time, but I'd also make it so the end of this green phase coincides with the end of the inflow of green wave cars, or maybe just a little later. So the first few green wave cars have to stop for a few seconds, but then the light turns green, and the rest of the pack gets through before it turns red again. A small fraction of the cars have experienced a very short delay. Not perfect, but really not a big deal. Now these cars cross the freeway, and two thirds of them enter the freeway on the left. The remaining cars, which are staying on the surface boulevard, encounter the next light. If it's set up like my earlier DDI Example 1, they will hit that light green, and continue on the boulevard, though slowing down for the swervy DDI might cause them to miss the light at the next mile-road. Or, maybe they get stopped at the second DDI light. As far as I'm concerned, they've changed to a different signal progression corridor, which doesn't have to be synchronized from the first one – though it probably will be, if this is a whole Detroitoid grid with progression on all the mile-roads. And anyway, we're talking about just 20% of the original incoming wave of cars.
But there's a good argument for why the second signal at a DDI doesn't have to be timed to let through all the cars coming from the first signal: there's
always cars coming from that other signal. The other signal is always sending it either left-turning freeway-exit traffic, or boulevard through traffic. It's going to cause approximately the same total delays for cars in those streams no matter when it turns red. So each signal in a DDI really only needs to be timed to accommodate the waves of cars coming towards the interchange from the boulevard on its own side of the freeway. In that sense, a DDI can easily be tuned to cause minimal interference with signal progression along a corridor that ends there.
Maybe I'll do another time-distance diagram for a DDI accounting for the slowdown required by the swervy geometry. It probably won't be until at least Tuesday, if I do it at all.
Additional thoughts:
Have you considered a Parclo A4 where traffic exiting the freeway and wishing to turn left must actually turn right and then U-turn? After all, that's how left-turn traffic from minor side streets is handled on a Detroitoid boulevard. A SPUI can be similarly modified.
If you insist on considering the boulevard on both sides of the freeway as a single corridor for signal progression purposes, large volumes of turning (exiting and entering) traffic at the freeway – the conditions where a DDI is favored – will be problematic in any case. With any interchange design that brings exiting traffic to a traffic signal, the stream of traffic leaving the interchange on the boulevard will be practically constant. Even a parclo B4 without signalized exit ramps (which may be problematic in other ways with heavy exiting traffic volumes) will even out the waves of traffic to a lesser degree. Timing of traffic signals on one side of the freeway will be almost irrelevant to timing of signals on the other side because of this.
If one is passing through the DDI entirely on the surface road, you should only get at most one of the lights red, not both. If you hit two red lights traversing the DDI, at least if it's timed like the one in Rochester, it means you turned left off the freeway, lost a race with a snail, or ran the red. In any case, going through a DDI at the speed limit is impossible anyways due to the curves at the crossovers (unless the speed limit is already 25).
NYSDOT has "no turn on red" signs on the left turns of its DDI, so I presume that a left on red would have been legal were it not for the sign.
One thing that always bothered me about the DDI is that two opposing directions of traffic must cross each other. To me, this is almost like split-phasing, where eastbound and westbound traffic have completely separate phases - thereby increasing delays for both directions. So yes a DDI really should only be used if the most important movement is surface street to freeway. Otherwise, use a different design.
I grew up in California, where as many here know, they extensively use the parclo A4. It seems that this is preferred to eliminate a situation where there are so many cars wishing to make a left turn onto the on-ramp, that it would block the left lane of through traffic on the arterial. (From what I remember this was the reason for converting some diamonds into SPUIs). You see this at many diamond interchanges. To me, it would seem that a parclo B4 could potentially have his problem as well. So if the left turning movement from surface street to freeway is particularly heavy, maybe a parclo A4 is the answer, otherwise use the parclo B4, as it would reduce signal delay on the arterial.
Quote from: vdeane on April 18, 2015, 12:19:35 AM
If one is passing through the DDI entirely on the surface road, you should only get at most one of the lights red, not both.
Adjacent signals often run higher cycle lengths to the DDI signals making it a crapshoot if you get stuck at the first DDI light. The video below shows green to red signal progression between the two DDI traffic signals along Bangerter Hwy in Utah. In this Utah example, it's common for drivers to experience back to back red lights while driving the main corridor.
QuoteUDOT DIVERGING DIAMOND INTERCHANGE (DDI) OBSERVATIONS AND EXPERIENCE:
Coordination of the DDI with adjacent signals is not easily done. Most DDIs need a lower cycle length than the adjacent signals. This may result in a vehicle having to stop at both the off ramp terminal and the next adjacent signal.
https://www.youtube.com/watch?v=RhazZu4xMeA
Quote from: vdeane on April 18, 2015, 12:19:35 AM
In any case, going through a DDI at the speed limit is impossible anyways due to the curves at the crossovers (unless the speed limit is already 25).
A driver cruising at 50 mph on Bangerter Hwy is forced to slow down to 25 mph to navigate the DDI. Slowing down traffic to 25 mph can be a good thing in downtown Manhttan, it's not great along Bangerter Hwy in Utah.
Quote from: mrsman on April 19, 2015, 04:48:33 PM
I grew up in California, where as many here know, they extensively use the parclo A4. It seems that this is preferred to eliminate a situation where there are so many cars wishing to make a left turn onto the on-ramp, that it would block the left lane of through traffic on the arterial. (From what I remember this was the reason for converting some diamonds into SPUIs). You see this at many diamond interchanges. To me, it would seem that a parclo B4 could potentially have his problem as well. So if the left turning movement from surface street to freeway is particularly heavy, maybe a parclo A4 is the answer, otherwise use the parclo B4, as it would reduce signal delay on the arterial.
Wouldn't a SPUI experience the same situation where there are so many cars wishing to make a left turn onto the on-ramp, that it would block the left lane of through traffic on the arterial? Drivers entering the freeway from a SPUI do so by making a left turn as well.
Also, permissve-protected left-turns at a SPUI are unheard of due to the complexity of the interchange. There are examples of permissive-protected left-turns at Parclo B4s which help reduce driver delays (and reduce the queue length of left-turning vehicles from the arterial, since some drivers will turn in gaps). Here's an example of a FYA at a Parclo B4 at I-69 & Saginaw Hwy outside Lansing, Michigan:
https://www.youtube.com/watch?v=doeEKXAoo_0
Quote from: tradephoric on April 19, 2015, 11:31:13 PM
Quote from: mrsman on April 19, 2015, 04:48:33 PM
I grew up in California, where as many here know, they extensively use the parclo A4. It seems that this is preferred to eliminate a situation where there are so many cars wishing to make a left turn onto the on-ramp, that it would block the left lane of through traffic on the arterial. (From what I remember this was the reason for converting some diamonds into SPUIs). You see this at many diamond interchanges. To me, it would seem that a parclo B4 could potentially have his problem as well. So if the left turning movement from surface street to freeway is particularly heavy, maybe a parclo A4 is the answer, otherwise use the parclo B4, as it would reduce signal delay on the arterial.
Wouldn't a SPUI experience the same situation where there are so many cars wishing to make a left turn onto the on-ramp, that it would block the left lane of through traffic on the arterial? Drivers entering the freeway from a SPUI do so by making a left turn as well.
I was thinking of a situation with extremely short left turn storage lanes. Basically, the road is wide enough for only one left turn lane, not two.
Check out this situation on Broadway, near Downtown LA.
http://goo.gl/maps/S024x
Here, as you scroll, 17th is the "service road" for I-10 west and 18th is the service road for I-10 east. The left turn pocket for either 18th or 17th is no more than half a block long. So if there are more people turning left than can fit in the turn pocket, the left thru lane will be blocked. The length of the left turn pocket is limited by the need to provide for the left turn for the other direction. Now, if this were somehow turned into a SPUI, the left turn lane from Broadway to 18th could begin even north of 17th, as 18th and 17th would become "single point". But with a traditional diamond, once the capacity of the turn pocket is reached, the left through lane will be blocked.
Of course, if the surface street were wider, we can have multiple turn lanes to alleviate the problem.
I am sure, though, that for every parclo B4, the left turn lanes are long and/or wide enough to maintain the capacity necessary for the freeway entrance. That is probably part of the design. But if is too expensive to widen the arterial's bridge over the freeway (or the arterial's underpass under the freeway), I think parclo A4 is the way to go - since there are no left turns at all.
There is a Parclo A4 along the TCH outside Vancouver where the signal only stops one direction, and has a left-side merge with the other carriageway.
(https://www.aaroads.com/forum/proxy.php?request=http%3A%2F%2Fi.imgur.com%2FjYQB1CR.png&hash=a998bca68ef4fa874169d5590579daa4f82a12c7)
Quote from: jakeroot on April 20, 2015, 12:44:55 AM
There is a Parclo A4 along the TCH outside Vancouver where the signal only stops one direction, and has a left-side merge with the other carriageway.
(https://www.aaroads.com/forum/proxy.php?request=http%3A%2F%2Fi.imgur.com%2FjYQB1CR.png&hash=a998bca68ef4fa874169d5590579daa4f82a12c7)
There is another Parclo A4 in Maryland (I-95 @ MD 175) where there are left side merges in both directions. The two carriageways of the cross-street are widely separated though.
https://www.google.com/maps/@39.1775854,-76.7921088,16z/data=!3m1!1e3
I have noticed the growth of the use of the DDI throughout Missouri myself as I have seen them built in numerous locations - Springfield is laden with them now, and even Joplin has one now at Range Line Road and the I-44 - I don't know that they are a fad. I do note that we are about to get another interchange along the I-44 with roundabouts on each side of the bridge at Prigmor Road two miles east of the I-49/MO249 junction - a junction also present at Longview Road and the I-49 in Kansas City.
The SPUI below demonstrates two points:
1. Adjacent intersections can limit the amount of left-turn queuing space available at the SPUI. In this example, Reisterstown Road was widened to accommodate both the SPUI left turn lanes and the left-turn lane at the adjacent intersection. With a Parclo B4, the design is conducive of longer left-turn storage space since the off-ramp signals need to be a far distance apart to accommodate the loop ramps (OTOH, with a SPUI the adjacent signal may only be a couple hundred feet away). .
2. At a SPUI, all traffic exiting the freeway does so from one off-ramp. This increases the likelihood that traffic will back up onto the freeway. With a Parclo B4, there are two off-ramps effectively doubling the queue space for exiting freeway traffic (reducing the likelihood that traffic will back up onto the freeway).
(https://www.aaroads.com/forum/proxy.php?request=http%3A%2F%2Fi478.photobucket.com%2Falbums%2Frr144%2Ftradephoric%2FTransportation%2520Pictures%2FRandom%2Funtitled77_zpsrrd1qtif.png&hash=09b6a5d31d00b388457cd4cfa75d6224ef2d198c)
https://www.google.com/maps/@39.3848461,-76.7346219,589m/data=!3m1!1e3
Regarding your point #2, a Parclo B4 wouldn't help much in this case...it's pretty clear that the vast majority of traffic on the off-ramp is trying to head north on Reisterstown Rd. That's a queue that would likely back up onto the Beltway even if this was a Parclo B4.
Quote from: froggie on May 02, 2015, 12:06:29 PM
Regarding your point #2, a Parclo B4 wouldn't help much in this case...it's pretty clear that the vast majority of traffic on the off-ramp is trying to head north on Reisterstown Rd. That's a queue that would likely back up onto the Beltway even if this was a Parclo B4.
I'm counting about 30 vehicles making a left turn off I-695 (and roughly 60 waiting to turn right). If you reduce the queue by 33%, that's significant.
Quote from: tradephoric on May 02, 2015, 12:25:41 PM
I'm counting about 30 vehicles making a left turn off I-695 (and roughly 60 waiting to turn right). If you reduce the queue by 33%, that's significant.
Or, y'know, you could just add another lane to the off-ramp and make it a optional-lane exit.
Without investigating the interchange in detail, not allowing the right-hand off-ramp lane to free-flow into the third lane that shows up 20 feet down the road also seems to be a serious deficiency that appears to have been deliberately introduced.
Quote from: lordsutch on May 02, 2015, 06:30:54 PM
Or, y'know, you could just add another lane to the off-ramp and make it a optional-lane exit.
Without investigating the interchange in detail, not allowing the right-hand off-ramp lane to free-flow into the third lane that shows up 20 feet down the road also seems to be a serious deficiency that appears to have been deliberately introduced.
Imagine a scenario where an off-ramp signal is stuck red during the PM rush. Would a SPUI or a Parclo B4 better manage this scenario? All traffic exiting the freeway at a Parclo B4 make a simple right-turn onto the arterial. That's a big advantage. There's a reason why there are many unsignalized Parclo B4 interchanges out there. It's just a simple design that reduces the likelihood that traffic will back up onto the freeway. Can you cite even one example of an unsignalized SPUI?
Quote from: tradephoric on May 02, 2015, 07:43:53 PM
Quote from: lordsutch on May 02, 2015, 06:30:54 PM
Or, y'know, you could just add another lane to the off-ramp and make it a optional-lane exit.
Without investigating the interchange in detail, not allowing the right-hand off-ramp lane to free-flow into the third lane that shows up 20 feet down the road also seems to be a serious deficiency that appears to have been deliberately introduced.
Imagine a scenario where an off-ramp signal is stuck red during the PM rush. Would a SPUI or a Parclo B4 better manage this scenario? All traffic exiting the freeway at a Parclo B4 make a simple right-turn onto the arterial. That's a big advantage. There's a reason why there are many unsignalized Parclo B4 interchanges out there. It's just a simple design that reduces the likelihood that traffic will back up onto the freeway. Can you cite even one example of an unsignalized SPUI?
Except if something is stuck on red for that long, there's a good chance it would register as a fault and send the thing into flash mode. Not ideal, I know, but many B4s are signalized with NTOR from the ramp. You'd have some of the same issues. A SPUI is almost always superior to a B4 just because the traffic entering the arterial is metered.
Quote from: cl94 on May 02, 2015, 08:25:31 PM
Except if something is stuck on red for that long, there's a good chance it would register as a fault and send the thing into flash mode. Not ideal, I know, but many B4s are signalized with NTOR from the ramp. You'd have some of the same issues. A SPUI is almost always superior to a B4 just because the traffic entering the arterial is metered.
Here's an example of a Parclo B4 with metered off ramps. Also, all traffic is allowed to make a right turn on red.
https://www.google.com/maps/@29.54,-95.1423654,686m/data=!3m1!1e3
Sounds to me like that Parclo could be affected with some of the same issues cross traffic drivers faced in Santa Barbara when US101 was signalised through downtown prior to 1991.
Quote from: tradephoric on May 02, 2015, 07:43:53 PM
Quote from: lordsutch on May 02, 2015, 06:30:54 PM
Or, y'know, you could just add another lane to the off-ramp and make it a optional-lane exit.
Without investigating the interchange in detail, not allowing the right-hand off-ramp lane to free-flow into the third lane that shows up 20 feet down the road also seems to be a serious deficiency that appears to have been deliberately introduced.
Imagine a scenario where an off-ramp signal is stuck red during the PM rush. Would a SPUI or a Parclo B4 better manage this scenario? All traffic exiting the freeway at a Parclo B4 make a simple right-turn onto the arterial. That's a big advantage. There's a reason why there are many unsignalized Parclo B4 interchanges out there. It's just a simple design that reduces the likelihood that traffic will back up onto the freeway. Can you cite even one example of an unsignalized SPUI?
Here's one (https://www.google.com/maps/@42.363871,-87.8288209,20z/data=!3m1!1e3), although it's admittedly on a dying expressway where the cross street might have more traffic than the expressway. :D
Quote from: PurdueBill on May 04, 2015, 06:45:53 PM
Here's one (https://www.google.com/maps/@42.363871,-87.8288209,20z/data=!3m1!1e3), although it's admittedly on a dying expressway where the cross street might have more traffic than the expressway. :D
I'm impressed Bill! How did u stumble upon this unsignalized SPUI? Here are some unsignalized Parclo B4 interchanges out there:
https://www.google.com/maps?ll=39.66336,-77.73976&z=17&t=h
https://www.google.com/maps/@34.72814,-86.6702,1296m/data=!3m1!1e3
https://www.google.com/maps?ll=43.17946,-71.53100&z=17&t=h
https://www.google.com/maps/@40.77906,-82.47048,1194m/data=!3m1!1e3
https://www.google.com/maps/@52.142707,-113.8139833,484m/data=!3m1!1e3
https://www.google.com/maps/@40.87241,-77.77835,1193m/data=!3m1!1e3
https://www.google.com/maps/@40.82006,-98.37846,1194m/data=!3m1!1e3
https://www.google.com/maps/@34.09093,-81.16557,653m/data=!3m1!1e3
https://www.google.com/maps/@39.93293,-76.68957,605m/data=!3m1!1e3
https://www.google.com/maps/@41.6661,-71.0932,589m/data=!3m1!1e3
https://www.google.com/maps/@35.76171,-78.02815,1280m/data=!3m1!1e3
https://www.google.com/maps/@41.1113,-100.76341,1188m/data=!3m1!1e3
https://www.google.com/maps/@46.75404,-71.42404,1081m/data=!3m1!1e3
https://www.google.com/maps/@35.0824,-85.20656,645m/data=!3m1!1e3
https://www.google.com/maps/@43.15426,-86.21083,1151m/data=!3m1!1e3
https://www.google.com/maps/@47.60011,-52.73229,1063m/data=!3m1!1e3
https://www.google.com/maps/@39.15734,-76.60406,611m/data=!3m1!1e3
https://www.google.com/maps/@37.75684,-79.40965,1247m/data=!3m1!1e3
https://www.google.com/maps/@42.9905,-82.34378,1154m/data=!3m1!1e3
https://www.google.com/maps/@42.2932,-82.92605,583m/data=!3m1!1e3
https://www.google.com/maps/@46.42746,-81.12091,1087m/data=!3m1!1e3
https://www.google.com/maps/@38.1583,-84.89337,1240m/data=!3m1!1e3
https://www.google.com/maps/@41.60732,-87.10798,1179m/data=!3m1!1e3
https://www.google.com/maps/@30.4853,-84.15839,1359m/data=!3m1!1e3
https://www.google.com/maps/@37.19931,-77.46347,1256m/data=!3m1!1e3
https://www.google.com/maps/@30.41204,-81.74739,1360m/data=!3m1!1e3
https://www.google.com/maps/@30.11086,-81.44671,1364m/data=!3m1!1e3
https://www.google.com/maps/@30.53699,-88.23993,679m/data=!3m1!1e3
https://www.google.com/maps/@39.66267,-83.94955,1214m/data=!3m1!1e3
https://www.google.com/maps/@34.39711,-92.82724,1301m/data=!3m1!1e3
https://www.google.com/maps/@39.30473,-85.96192,1220m/data=!3m1!1e3
https://www.google.com/maps/@39.83323,-84.81687,1211m/data=!3m1!1e3
https://www.google.com/maps/@61.22703,-149.73356,380m/data=!3m1!1e3
https://www.google.com/maps/@40.76559,-73.68983,597m/data=!3m1!1e3
https://www.google.com/maps/@40.83691,-96.71197,1193m/data=!3m1!1e3
https://www.google.com/maps/@37.97293,-84.8753,1243m/data=!3m1!1e3
https://www.google.com/maps/@44.03049,-92.48802,1134m/data=!3m1!1e3
https://www.google.com/maps/@37.85138,-122.0285,623m/data=!3m1!1e3
And here's an unsignalized Parclo B4 servicing a major 6-lane boulevard:
https://www.google.com/maps/@27.90329,-82.3428,1394m/data=!3m1!1e3
Quote from: PurdueBill on May 04, 2015, 06:45:53 PM
Here's one (https://www.google.com/maps/@42.363871,-87.8288209,20z/data=!3m1!1e3), although it's admittedly on a dying expressway where the cross street might have more traffic than the expressway. :D
By the way, this is a perfect example of how adjacent intersections can limit the left-turn queuing space. The adjacent intersection is only 300 feet away from the SPUI, and the left-turn lane is only 50 feet long (just enough space for 2 or 3 vehicles to squeeze in).
Quote from: tradephoric on May 04, 2015, 08:44:19 PM
Quote from: PurdueBill on May 04, 2015, 06:45:53 PM
Here's one (https://www.google.com/maps/@42.363871,-87.8288209,20z/data=!3m1!1e3), although it's admittedly on a dying expressway where the cross street might have more traffic than the expressway. :D
I'm impressed Bill! How did u stumble upon this unsignalized SPUI?3
I was
so close to finding this intersection, but instead I found the northern end of the Amstutz, which is also a stop-sign controlled half SPUI (though it's technically an abandoned full SPUI). I didn't bother to look any farther south. I kind of wish I had now.
FWIW, these are a couple of the oldest SPUIs in the country (I believe the first one was in Florida, but both the one in Florida and these in Illinois were built in the 70s).
One of the largest DDI's is about to be constructed in Florida. With so much through traffic along the main corridor, is this really the best location for a DDI? Got to love that green-to-red signal progression drivers get to enjoy. What a thrill.
https://www.youtube.com/watch?v=24jMVZszPTY#
Quote from: tradephoric on August 04, 2015, 11:45:53 AM
One of the largest DDI's is about to be constructed in Florida. With so much through traffic along the main corridor
How do you know it's not turning off within a mile of the interchange?
PARCLO B4
Quote from: NE2 on August 04, 2015, 12:34:11 PM
Quote from: tradephoric on August 04, 2015, 11:45:53 AM
One of the largest DDI's is about to be constructed in Florida. With so much through traffic along the main corridor
How do you know it's not turning off within a mile of the interchange?
PARCLO B4
I agree. A Parclo B4 would be a better choice for this interchange. Thank you.
Quote from: tradephoric on August 04, 2015, 01:26:02 PM
Quote from: NE2 on August 04, 2015, 12:34:11 PM
Quote from: tradephoric on August 04, 2015, 11:45:53 AM
One of the largest DDI's is about to be constructed in Florida. With so much through traffic along the main corridor
How do you know it's not turning off within a mile of the interchange?
PARCLO B4
I agree. A Parclo B4 would be a better choice for this interchange. Thank you.
Not enough room for it. Only quadrant that could easily fit a loop with a decent radius. The DDI could be built within the footprint of the current interchange, while a B4 would require relocation of retention ponds (not easy) and land acquisition.
Quote from: cl94 on August 04, 2015, 01:35:06 PM
Not enough room for it. Only quadrant that could easily fit a loop with a decent radius. The DDI could be built within the footprint of the current interchange, while a B4 would require relocation of retention ponds (not easy) and land acquisition.
Just extend the loop ramp farther out. It would require more ROW acquisition but the advantage is the I-75 bridge would not need to be widened to accommodate the deceleration lane. Even if a Parclo B4 costs more money, it would have operational advantages over the DDI. Cost isn't the only factor when deciding which type of interchange design to choose (and for all we know the Parclo B4 would be cheaper).
(https://www.aaroads.com/forum/proxy.php?request=http%3A%2F%2Fi478.photobucket.com%2Falbums%2Frr144%2Ftradephoric%2FTransportation%2520Pictures%2FRandom%2Ffloridaparclo_zpsmzmim2wp.jpg&hash=5669cae6c64859c541b14bd4fae30cc8a5e42de5)
Quote from: tradephoric on August 04, 2015, 03:19:04 PM
Quote from: cl94 on August 04, 2015, 01:35:06 PM
Not enough room for it. Only quadrant that could easily fit a loop with a decent radius. The DDI could be built within the footprint of the current interchange, while a B4 would require relocation of retention ponds (not easy) and land acquisition.
Just extend the loop ramp farther out. It would require more ROW acquisition but the advantage is the I-75 bridge would not need to be widened to accommodate the deceleration lane. Even if a Parclo B4 costs more money, it would have operational advantages over the DDI. Cost isn't the only factor when deciding which type of interchange design to choose (and for all we know the Parclo B4 would be cheaper).
Kinda like green-to-red signal progression isn't the only factor when deciding which type of interchange design to choose.
Jeffandnicole, your implication that i only care about signal progression is wrong. In a previous post, I cited a study comparing the average delay per vehicle for a number of different interchange alternatives for I-695 at US 40. Drivers averaged an additional 60 seconds delay at the DDI compared to the Parclo B4.
What measure of effectiveness would you use? Just pick the interchange design that maximizes driver delays? No thanks.
Quote from: tradephoric on April 13, 2015, 04:34:54 PM
The I-695 at US 40 folded interchange study (linked in the previous post) looked at the average delay per vehicle for a number of different interchange alternatives. The existing Parclo B4 had 15 second average delay per vehicle compared to roughly 75 second for the DDI.
(https://www.aaroads.com/forum/proxy.php?request=http%3A%2F%2Fi478.photobucket.com%2Falbums%2Frr144%2Ftradephoric%2FTransportation%2520Pictures%2FRandom%2FLOS_zps40v02ztw.png&hash=7be851b8168dcfcef390abf7654735809a7e6491)
Quote from: tradephoric on August 04, 2015, 04:26:52 PM
Jeffandnicole, your implication that i only care about signal progression is wrong. In a previous post, I cited a study comparing the average delay per vehicle for a number of different interchange alternatives for I-695 at US 40. Drivers averaged an additional 60 seconds delay at the DDI compared to the Parclo B4.
What measure of effectiveness would you use? Just pick the interchange design that maximizes driver delays? No thanks.
Quote from: tradephoric on April 13, 2015, 04:34:54 PM
The I-695 at US 40 folded interchange study (linked in the previous post) looked at the average delay per vehicle for a number of different interchange alternatives. The existing Parclo B4 had 15 second average delay per vehicle compared to roughly 75 second for the DDI.
(https://www.aaroads.com/forum/proxy.php?request=http%3A%2F%2Fi478.photobucket.com%2Falbums%2Frr144%2Ftradephoric%2FTransportation%2520Pictures%2FRandom%2FLOS_zps40v02ztw.png&hash=7be851b8168dcfcef390abf7654735809a7e6491)
I'm sure a study of a single location can be applied universally.
Quote from: Rothman on August 04, 2015, 06:46:01 PM
Quote from: tradephoric on August 04, 2015, 04:26:52 PM
Jeffandnicole, your implication that i only care about signal progression is wrong. In a previous post, I cited a study comparing the average delay per vehicle for a number of different interchange alternatives for I-695 at US 40. Drivers averaged an additional 60 seconds delay at the DDI compared to the Parclo B4.
What measure of effectiveness would you use? Just pick the interchange design that maximizes driver delays? No thanks.
Quote from: tradephoric on April 13, 2015, 04:34:54 PM
The I-695 at US 40 folded interchange study (linked in the previous post) looked at the average delay per vehicle for a number of different interchange alternatives. The existing Parclo B4 had 15 second average delay per vehicle compared to roughly 75 second for the DDI.
(https://www.aaroads.com/forum/proxy.php?request=http%3A%2F%2Fi478.photobucket.com%2Falbums%2Frr144%2Ftradephoric%2FTransportation%2520Pictures%2FRandom%2FLOS_zps40v02ztw.png&hash=7be851b8168dcfcef390abf7654735809a7e6491)
I'm sure a study of a single location can be applied universally.
Yep. Similar to how a B4 is always superior. I'd need to see the reports, but my educated opinion would be that the DDI would be both cheaper and more effective in this situation. FDOT has several B4s and each has a much larger footprint than the currently available land. Judging by how other B4s in the state are laid out, no quadrant has enough room to fit a loop without buying up a ton of land or greatly decreasing curve radii. I'm assuming the space constraint
was the main motivation for a DDI in the first place.
Quote from: cl94 on May 02, 2015, 08:25:31 PM
Except if something is stuck on red for that long, there's a good chance it would register as a fault and send the thing into flash mode. Not ideal, I know, but many B4s are signalized with NTOR from the ramp. You'd have some of the same issues. A SPUI is almost always superior to a B4 just because the traffic entering the arterial is metered.
Your main rationale to why a SPUI is "˜almost always superior to a B4" is because off ramp traffic is metered? I have cited examples of B4s that have metered off ramps. Secondly, in the study cited the SPUI had an average delay of 82 seconds vs. an average delay of 15 seconds for the Parclo B4. Either you don't put much importance on driver delay or I found a major outlier to your "SPUI's are almost always superior to a B4" statement.
Quote from: cl94 on August 04, 2015, 07:11:53 PM
I'd need to see the reports, but my educated opinion would be that the DDI would be both cheaper and more effective in this situation.
The DDI would be more effective at delaying drivers. If you disagree, cite your own studies and report that bolster your argument. Your educated opinion isn't enough.
Quote from: tradephoric on August 04, 2015, 08:15:55 PM
Quote from: cl94 on May 02, 2015, 08:25:31 PM
Except if something is stuck on red for that long, there's a good chance it would register as a fault and send the thing into flash mode. Not ideal, I know, but many B4s are signalized with NTOR from the ramp. You'd have some of the same issues. A SPUI is almost always superior to a B4 just because the traffic entering the arterial is metered.
Your main rationale to why a SPUI is "˜almost always superior to a B4" is because off ramp traffic is metered? I have cited examples of B4s that have metered off ramps. Secondly, in the study cited the SPUI had an average delay of 82 seconds vs. an average delay of 15 seconds for the Parclo B4. Either you don't put much importance on driver delay or I found a major outlier to your "SPUI's are almost always superior to a B4" statement.
Quote from: cl94 on August 04, 2015, 07:11:53 PM
I'd need to see the reports, but my educated opinion would be that the DDI would be both cheaper and more effective in this situation.
The DDI would be more effective at delaying drivers. If you disagree, cite your own studies and report that bolster your argument. Your educated opinion isn't enough.
It all depends on the situation. If there's a lot of traffic turning left onto the expressway, they will stop at no more than one light. At a B4, they'd likely be stopped by at least one. Through traffic at a DDI has one light max.
If land prices at the interchange are high, cost would be significantly less. Construction could be completed with little impact to traffic (you'd basically be rerouting the ramps slightly and installing islands, the latter of which can be done last). If the delays are related to turning traffic, they'd be better at a DDI than they currently are.
Are those freeway-exiting loop ramps? 70 mph traffic slowing to 20-30 in a few hundred feet will get you some pretty spectacular GTA stunts on a regular basis, particularly without an uphill grade to slow exiting traffic down.
Quote from: tradephoric on August 04, 2015, 08:15:55 PM
Quote from: cl94 on May 02, 2015, 08:25:31 PM
Except if something is stuck on red for that long, there's a good chance it would register as a fault and send the thing into flash mode. Not ideal, I know, but many B4s are signalized with NTOR from the ramp. You'd have some of the same issues. A SPUI is almost always superior to a B4 just because the traffic entering the arterial is metered.
Your main rationale to why a SPUI is ‘almost always superior to a B4" is because off ramp traffic is metered? I have cited examples of B4s that have metered off ramps. Secondly, in the study cited the SPUI had an average delay of 82 seconds vs. an average delay of 15 seconds for the Parclo B4. Either you don’t put much importance on driver delay or I found a major outlier to your “SPUI’s are almost always superior to a B4” statement.
Quote from: cl94 on August 04, 2015, 07:11:53 PM
I'd need to see the reports, but my educated opinion would be that the DDI would be both cheaper and more effective in this situation.
The DDI would be more effective at delaying drivers. If you disagree, cite your own studies and report that bolster your argument. Your educated opinion isn’t enough.
You cited a single study at a single interchange not even related to this interchange.
Quote from: lordsutch on August 05, 2015, 01:48:47 AM
Are those freeway-exiting loop ramps? 70 mph traffic slowing to 20-30 in a few hundred feet will get you some pretty spectacular GTA stunts on a regular basis, particularly without an uphill grade to slow exiting traffic down.
Good point. Didn't even think of that. They'd have to replace the bridges to add deceleration lanes if it became a B4. There isn't nearly enough room for such lanes if they began after the bridge.
Quote from: jeffandnicole on August 05, 2015, 06:27:27 AM
You cited a single study at a single interchange not even related to this interchange.
I cited the I-695 & US 40 study because you implied that i was only concern was about signal progression. My comments on the study repudiates that implication since they focus on LOS and average driver delay (with no mention of signal progression). These are pretty standard measures of effectiveness. What measures of effectiveness are acceptable to you?
Quote from: tradephoric on August 05, 2015, 10:24:27 AM
Quote from: jeffandnicole on August 05, 2015, 06:27:27 AM
You cited a single study at a single interchange not even related to this interchange.
I cited the I-695 & US 40 study because you implied that i was only concern was about signal progression. My comments on the study repudiates that implication since they focus on LOS and average driver delay (with no mention of signal progression). These are pretty standard measures of effectiveness. What measures of effectiveness are acceptable to you?
Heh. The measures are fine. The sampling is not.
Quote from: cl94 on August 05, 2015, 07:46:51 AM
Quote from: lordsutch on August 05, 2015, 01:48:47 AM
Are those freeway-exiting loop ramps? 70 mph traffic slowing to 20-30 in a few hundred feet will get you some pretty spectacular GTA stunts on a regular basis, particularly without an uphill grade to slow exiting traffic down.
Good point. Didn't even think of that. They'd have to replace the bridges to add deceleration lanes if it became a B4. There isn't nearly enough room for such lanes if they began after the bridge.
I disagree. Your assumption is the loop ramp would begin immediately after the bridge deck. In the B4 sketchup, the loop for NB I-75 doesn't begin till roughly 1300 feet past the bridge deck. That gives plenty of room for a deceleration lane without the need to widen the bridge out.
Quote from: tradephoric on August 05, 2015, 10:47:56 AM
Quote from: cl94 on August 05, 2015, 07:46:51 AM
Quote from: lordsutch on August 05, 2015, 01:48:47 AM
Are those freeway-exiting loop ramps? 70 mph traffic slowing to 20-30 in a few hundred feet will get you some pretty spectacular GTA stunts on a regular basis, particularly without an uphill grade to slow exiting traffic down.
Good point. Didn't even think of that. They'd have to replace the bridges to add deceleration lanes if it became a B4. There isn't nearly enough room for such lanes if they began after the bridge.
I disagree. Your assumption is the loop ramp would begin immediately after the bridge deck. In the B4 sketchup, the loop for NB I-75 doesn't begin till roughly 1300 feet past the bridge deck. That gives plenty of room for a deceleration lane without the need to widen the bridge out.
But what about the SB loop ramp? No room for a deceleration lane and the radius would still be below what FDOT typically uses
Quote from: cl94 on August 05, 2015, 12:49:02 PM
But what about the SB loop ramp? No room for a deceleration lane and the radius would still be below what FDOT typically uses
Again, your assumption is the loop ramp would begin immediately after the bridge deck. The final FDOT design probably wouldn't match my two minute sketch up. The SB loop could mirror the NB loop if you want to avoid bridge widenings. Also, the radius of the loops in the sketch is larger than the surrounding loops along I-75. There is enough room to fit a properly sized Parclo B4 at this location.
Quote from: tradephoric on August 05, 2015, 01:30:34 PM
Quote from: cl94 on August 05, 2015, 12:49:02 PM
But what about the SB loop ramp? No room for a deceleration lane and the radius would still be below what FDOT typically uses
Again, your assumption is the loop ramp would begin immediately after the bridge deck. The final FDOT design probably wouldn't match my two minute sketch up. The SB loop could mirror the NB loop if you want to avoid bridge widenings. Also, the radius of the loops in the sketch is larger than the surrounding loops along I-75. There is enough room to fit a properly sized Parclo B4 at this location.
I'm also thinking from a DOT and PR perspecrive. The public won't take kindly to the state taking over a large portion of the barrier separating the expressway from homes and businesses. Not only would ramps be longer, but you'd have to design and install drainage systems, landscape, and maintain more pavement.
Do you have some sort of vendetta against DDIs? Are DDIs taking your business away?
^You are focused on the footprint of the interchange and I'm focused on driver delay. I'd rather have a large interchange that minimizes driver delay as opposed to a small interchange that maximizes driver delay.
Cost-benefit analysis. I'd need the report to confirm, but I assume land values are high and any simulated delay does not overcome the increased cost of constructing a B4. If I had FDOT's intersection count data, I could toss everything in VISSIM and compare delays.
Quote from: cl94 on August 05, 2015, 04:28:43 PM
Do you have some sort of vendetta against DDIs? Are DDIs taking your business away?
FYI: I don't think I've ever seen a post from tradephoric that wasn't about green wave signal progression or parclo B4s (ESPECIALLY parclo B4s).
Quote from: vdeane on August 05, 2015, 09:01:23 PM
Quote from: cl94 on August 05, 2015, 04:28:43 PM
Do you have some sort of vendetta against DDIs? Are DDIs taking your business away?
FYI: I don't think I've ever seen a post from tradephoric that wasn't about green wave signal progression or parclo B4s (ESPECIALLY parclo B4s).
DDIs and roundabouts are the other 2 main things they post about, but posts for both relate to the above 2 topics. There's a reason why Canada uses A4s instead of B4s.
Quote from: cl94 on August 05, 2015, 09:05:56 PM
Quote from: vdeane on August 05, 2015, 09:01:23 PM
Quote from: cl94 on August 05, 2015, 04:28:43 PM
Do you have some sort of vendetta against DDIs? Are DDIs taking your business away?
FYI: I don't think I've ever seen a post from tradephoric that wasn't about green wave signal progression or parclo B4s (ESPECIALLY parclo B4s).
DDIs and roundabouts are the other 2 main things they post about, but posts for both relate to the above 2 topics. There's a reason why Canada uses A4s instead of B4s.
I started a roundabout thread that discusses the crash rates of multi-lane roundabouts. In 10 pages of posts, not once did i mention green waves or Parclo B4s. Roundabouts actually destroys signal progression. If I was obsessed with green waves, why would I be actively promoting modern roundabouts that destroy them? Sure, I was critical of a lot of high crash rate modern roundabouts in the thread, but the focus was to increasing the size of the ICD to reduce the crash rate (not to rip them out and replace them with traffic signals).
I do wondered why there are so many A4s in Canada (they only have a few examples of B4s). OTOH, America has over 100 Parclo B4 interchanges and it is much more common. Why is Canada so hesitant to designing Parclo B4s? Do Canadian drivers take comfort in getting stopped at red lights?
Quote from: tradephoric on August 06, 2015, 11:17:09 AM
Quote from: cl94 on August 05, 2015, 09:05:56 PM
Quote from: vdeane on August 05, 2015, 09:01:23 PM
Quote from: cl94 on August 05, 2015, 04:28:43 PM
Do you have some sort of vendetta against DDIs? Are DDIs taking your business away?
FYI: I don't think I've ever seen a post from tradephoric that wasn't about green wave signal progression or parclo B4s (ESPECIALLY parclo B4s).
DDIs and roundabouts are the other 2 main things they post about, but posts for both relate to the above 2 topics. There's a reason why Canada uses A4s instead of B4s.
I started a roundabout thread that discusses the crash rates of multi-lane roundabouts. In 10 pages of posts, not once did i mention green waves or Parclo B4s. Roundabouts actually destroys signal progression. If I was obsessed with green waves, why would I be actively promoting modern roundabouts that destroy them? Sure, I was critical of a lot of high crash rate modern roundabouts in the thread, but the focus was to increasing the size of the ICD to reduce the crash rate (not to rip them out and replace them with traffic signals).
I do wondered why there are so many A4s in Canada (they only have a few examples of B4s). OTOH, America has over 100 Parclo B4 interchanges and it is much more common. Why is Canada so hesitant to designing Parclo B4s? Do Canadian drivers take comfort in getting stopped at red lights?
Few reasons:
1. Exit ramp is long and straight, providing space for deceleration and reducing the chance of accidents.
2. Turning traffic typically doesn't have to turn cross the path of opposing traffic.
3. All entrances are on the right, providing consistency.
4. Fewer exits from the expressway. Standard is to keep the number of departure points as low as possible.
I wouldn't say that B4s are much more common. I know of a lot of A4s in the northeast. probably more A4s around here than B4s.
Quote from: tradephoric on August 05, 2015, 05:52:31 PM
^You are focused on the footprint of the interchange and I’m focused on driver delay. I’d rather have a large interchange that minimizes driver delay as opposed to a small interchange that maximizes driver delay.
In a perfect world, there would be cheap solutions that would minimize driver delay. We would have 20 lane-wide roadways that never congest. In the real world, it doesn't happen. If you were to tell a bunch of people their development was going to be wiped out, and others would be living right next to a ramp, so that drivers on the main road would save a few seconds of time, your idea would go absolutely nowhere. When you're dealing with limited space, environmental issues, ROW issues, and a whole bunch of other situations, you can't simply look at a design that simply focuses on one thing.
In the road-building world, there is a LOT of give and take. The most optimal design is rarely built because of a host of other factors.
Quote from: jeffandnicole on August 06, 2015, 12:40:05 PM
Quote from: tradephoric on August 05, 2015, 05:52:31 PM
^You are focused on the footprint of the interchange and I'm focused on driver delay. I'd rather have a large interchange that minimizes driver delay as opposed to a small interchange that maximizes driver delay.
In a perfect world, there would be cheap solutions that would minimize driver delay. We would have 20 lane-wide roadways that never congest. In the real world, it doesn't happen. If you were to tell a bunch of people their development was going to be wiped out, and others would be living right next to a ramp, so that drivers on the main road would save a few seconds of time, your idea would go absolutely nowhere. When you're dealing with limited space, environmental issues, ROW issues, and a whole bunch of other situations, you can't simply look at a design that simply focuses on one thing.
In the road-building world, there is a LOT of give and take. The most optimal design is rarely built because of a host of other factors.
Agree completely. Many of those you're debating against (myself included) work in the field, whether it be at a DOT, MPO, or private consulting firm. You might not think it, but just from pictures I know the extent of ROW and environmental issues. There's a balance between delay and cost. Usually, the proposals at any extreme are unacceptable because the balance is not met. You need to be able to sell it to the public. Here, i think the DDI is easier to sell. Hell, being at an MPO, that's a huge part of my job-selling it to the public.
Quote from: jeffandnicole on August 06, 2015, 12:40:05 PMIn a perfect world, there would be cheap solutions that would minimize driver delay. We would have 20 lane-wide roadways that never congest. In the real world, it doesn't happen.
Well, it sometimes happens ;).
(https://www.aaroads.com/forum/proxy.php?request=http%3A%2F%2Fi478.photobucket.com%2Falbums%2Frr144%2Ftradephoric%2FTransportation%2520Pictures%2FWide%2520streets%2F120108_677_zps14c8e00b.jpg&hash=f3a30d073c0b7bad57aa7089f74bbf349e25c2c7)
Quote from: jeffandnicole on August 06, 2015, 12:40:05 PM
If you were to tell a bunch of people their development was going to be wiped out, and others would be living right next to a ramp, so that drivers on the main road would save a few seconds of time, your idea would go absolutely nowhere. When you're dealing with limited space, environmental issues, ROW issues, and a whole bunch of other situations, you can't simply look at a design that simply focuses on one thing.
In the road-building world, there is a LOT of give and take. The most optimal design is rarely built because of a host of other factors.
These are all legitimate points. My focus on operational efficiency was due to CL94 saying that they believed the DDI would be "˜both cheaper and more effective' in this situation. After this comment, I'm entitled to make my point why I believe a DDI wouldn't be more effective than a Parclo B4 (even if the cost of the B4 would be exorbitantly high). I realize cost is a big consideration though. Just a few posts back I cited an example of an interchange on Pleasant Hill Road in Atlanta where a Parclo B4 would have been cost prohibitive.
Quote from: tradephoric on August 06, 2015, 01:37:30 PM
Well, it sometimes happens ;).
(https://www.aaroads.com/forum/proxy.php?request=http%3A%2F%2Fi478.photobucket.com%2Falbums%2Frr144%2Ftradephoric%2FTransportation%2520Pictures%2FWide%2520streets%2F120108_677_zps14c8e00b.jpg&hash=f3a30d073c0b7bad57aa7089f74bbf349e25c2c7)
Not to change the subject, but what is this photo? Parking waiting for a ferryboat or loading/unloading cars from a ship?
Quote from: kkt on August 06, 2015, 02:19:48 PM
Quote from: tradephoric on August 06, 2015, 01:37:30 PM
Well, it sometimes happens ;).
(https://www.aaroads.com/forum/proxy.php?request=http%3A%2F%2Fi478.photobucket.com%2Falbums%2Frr144%2Ftradephoric%2FTransportation%2520Pictures%2FWide%2520streets%2F120108_677_zps14c8e00b.jpg&hash=f3a30d073c0b7bad57aa7089f74bbf349e25c2c7)
Not to change the subject, but what is this photo? Parking waiting for a ferryboat or loading/unloading cars from a ship?
Makes me wonder if it's the circle road around Moscow.
Quote from: kkt on August 06, 2015, 02:19:48 PM
Quote from: tradephoric on August 06, 2015, 01:37:30 PM
Well, it sometimes happens ;).
[image snipped]
Not to change the subject, but what is this photo? Parking waiting for a ferryboat or loading/unloading cars from a ship?
It's a road in North Korea. Their "dear leader" built these massive 401 sized highways that nearly no one drives on, I guess to make it look like their country has great infrastructure to the people of the country.
Quote from: kkt on August 06, 2015, 02:19:48 PM
Not to change the subject, but what is this photo? Parking waiting for a ferryboat or loading/unloading cars from a ship?
http://www.google.com/maps/@19.776228,96.1302704,217m/data=!3m1!1e3
Quote from: NE2 on August 06, 2015, 02:45:47 PM
Quote from: kkt on August 06, 2015, 02:19:48 PM
Not to change the subject, but what is this photo? Parking waiting for a ferryboat or loading/unloading cars from a ship?
http://www.google.com/maps/@19.776228,96.1302704,217m/data=!3m1!1e3
Thanks... I was going to go find it... That's just idiotic
Quote from: kkt on August 06, 2015, 02:19:48 PM
Not to change the subject, but what is this photo? Parking waiting for a ferryboat or loading/unloading cars from a ship?
It's a road near Myanmar's parliament building. I believe the road doubles up as a landing strip for military planes.
Top Gear did a show where they were driving on this road. They got out and played a soccer game in the middle of the street.
Quote from: NE2 on August 06, 2015, 02:45:47 PM
Quote from: kkt on August 06, 2015, 02:19:48 PM
Not to change the subject, but what is this photo? Parking waiting for a ferryboat or loading/unloading cars from a ship?
http://www.google.com/maps/@19.776228,96.1302704,217m/data=!3m1!1e3
Wow, I was way off. North Korea has roads that look similar to this.
Quote from: cl94 on August 06, 2015, 12:28:22 PM
Quote from: tradephoric on August 06, 2015, 11:17:09 AM
I do wondered why there are so many A4s in Canada (they only have a few examples of B4s). OTOH, America has over 100 Parclo B4 interchanges and it is much more common. Why is Canada so hesitant to designing Parclo B4s? Do Canadian drivers take comfort in getting stopped at red lights?
Few reasons:
1. Exit ramp is long and straight, providing space for deceleration and reducing the chance of accidents.
2. Turning traffic typically doesn't have to turn cross the path of opposing traffic.
3. All entrances are on the right, providing consistency.
4. Fewer exits from the expressway. Standard is to keep the number of departure points as low as possible.
I wouldn't say that B4s are much more common. I know of a lot of A4s in the northeast. probably more A4s around here than B4s.
There are counter-points to consider:
1. Exit ramp is long and straight, providing space for deceleration and reducing the chance of accidents.With a Parclo A4, the difference in speeds of entering loop traffic and freeway traffic is high. A semi-truck entering the freeway is doing 25 mph in the acceleration lane as freeway traffic is cruising past at 70 mph. The difference in speeds is 45 mph. In addition, there are two entrance ramps at a Parclo A4 leading to two merge points (leading to additional merging conflict points).
2. Turning traffic typically doesn't have to turn cross the path of opposing traffic.While entering drivers don't have to cross the path of opposing traffic, exiting traffic on a Parclo A4 must cross two directions of opposing traffic (not just one). The Parclo B4 has similar design elements as a Restricted Crossing U-Turn Intersection which has a proven safety record. Researchers from North Carolina State University have found that RCUTs reduce total accidents by 46% and reduce personal injury accidents by 63% when compared to conventional intersection designs. The Parclo A4 behaves more like a standard signalized intersection.
3. All entrances are on the right, providing consistency.Drivers along major corridors are constantly making left turns (so a left turn entrance ramp isn't really out of the ordinary). In addition, by having two entrance ramps on opposing sides of the road, it helps distribute traffic more evenly along the corridor. This prevents drivers from wanting to all merge to the right to get onto the freeway (like you see at Parclo A4s). Uneven queuing along a corridor can lead to dangerous situations.
4. Fewer exits from the expressway. Standard is to keep the number of departure points as low as possible.Wouldn't it be more beneficial to reduce the number of entry points onto a freeway? If I'm a semi driver on the freeway, I'd rather only have to deal with one entrance ramp of merging traffic as opposed to two. The Parclo B4 has one entrance ramp.
Quote from: NE2 on August 06, 2015, 02:45:47 PM
http://www.google.com/maps/@19.776228,96.1302704,217m/data=!3m1!1e3
Panning shows it ending on the left with a T-intersection with a narrow road, and panning right shows some narrowing but with a roundabout with many lanes right after that
Quote from: tradephoric on August 06, 2015, 03:27:25 PM
3. All entrances are on the right, providing consistency.
Drivers along major corridors are constantly making left turns (so a left turn entrance ramp isn't really out of the ordinary). In addition, by having two entrance ramps on opposing sides of the road, it helps distribute traffic more evenly along the corridor. This prevents drivers from wanting to all merge to the right to get onto the freeway (like you see at Parclo A4s). Uneven queuing along a corridor can lead to dangerous situations.
4. Fewer exits from the expressway. Standard is to keep the number of departure points as low as possible.
Wouldn't it be more beneficial to reduce the number of entry points onto a freeway? If I'm a semi driver on the freeway, I'd rather only have to deal with one entrance ramp of merging traffic as opposed to two. The Parclo B4 has one entrance ramp.
With regard to point 3, it is especially important that the local jurisdictions adequately sign what lane you have to be in to access the freeway. They do this very well in L.A.
See: https://www.google.com/maps/@33.881928,-118.352545,3a,75y,350.29h,72.67t/data=!3m6!1e1!3m4!1sTT0wj20wL9dqNTMR7skZTw!2e0!7i13312!8i6656!6m1!1e1
I particularly chose this example, becuase the ramps here are counterintuitive. If this were a diamond interchange, South would be right and North would be left. But since the ramps are trumpets instead, the directions are reversed. So it is critical that the advanced warning sign is big, particularly as Hawthorne Blvd is 4 lanes in the northbound direction and you may need time to get over to the proper lane.
With regard to 4, generally entrances cause more disruption to the freeway traffic than entrances, so with all other things being equal it would be better to minimize the number of entrances over the exits.
Of course, there are many factors involved in deciding what is the best interchange type for any given situation.
Looks like Canada is getting into the diverging diamond action. This one's construction will start next year and finish in 2017.
http://www.metronews.ca/news/calgary/2015/06/21/calgary-to-build-first-diverging-diamond-interchange-with-traffic-on-left-side.html
There is also this one which may or may not be built:
http://www.highways.gov.sk.ca/Default.aspx?DN=50cd8830-902a-4bd4-8231-bf54ca6d6acf
DDI's are becoming more popular here in the Charlotte area. 3 have just recently been constructed and 1 is being built to replace the current clover in Concord off I-85. They all seem to be pretty efficient so far and due to their cost and smaller footprint, will not be going away anytime soon.
Here's a KMZ file of all known DDI's in America (64 total):
https://www.mediafire.com/?e5ze6t90ftqgv9h
Quote from: tradephoric on February 08, 2016, 05:29:11 PM
Here's a KMZ file of all known DDI's in America (64 total):
https://www.mediafire.com/?e5ze6t90ftqgv9h
Great map, Trade. Thanks. Looks like some states are more into them than others (looking at you, Utah).
I wonder what Utah has to say about their DDIs? Have they performed any before/after studies?
Quote from: jakeroot on February 08, 2016, 05:38:03 PM
Great map, Trade. Thanks. Looks like some states are more into them than others (looking at you, Utah).
I wonder what Utah has to say about their DDIs? Have they performed any before/after studies?
Thanks Jake. Utah did put together a Guide to Diverging Diamond Interchanges. Here's the opening paragraph of the executive summary:
QuoteReflecting on human tendencies, Abraham Maslow once said, "I suppose it is tempting, if the only tool you have is a hammer, to treat everything as if it were a nail." This maxim, known as Maslow's Hammer, has been frequently observed in science and engineering fields. As new innovations are introduced and applied, they sometimes struggle for initial acceptance but then gain in popularity until they are often over-applied.
.....
Despite this initial success, the DDI is not a one size fits all solution, and it is certainly not the Department's only tool for improving interchanges. Thus, it is important to reiterate that while the DDI has performed very well at some locations, it has failed to impress at others. While it has been a valuable congestion mitigation solution under favorable traffic conditions, it has not fully met expectations in less favorable conditions. Consequently, the DDI may not be appropriate when compared to other interchange types in these less unfavorable circumstances.
http://www.udot.utah.gov/main/uconowner.gf?n=14769524027177477
This doesn't sound like a ringing endorsement for the DDI. The opening paragraph suggests that the DDI is becoming over-applied. The reference to "Maslow's Hammer" is telling. It also states that some DDIs "failed to impress" at some locations. Such strong language could have easily been avoided but they decided to include it. That's telling. It just doesn't seem like Utah is overly impressed.
Quote from: tradephoric on February 08, 2016, 08:10:25 PM
This doesn't sound like a ringing endorsement for the DDI. The opening paragraph suggests that the DDI is becoming over-applied. The reference to "Maslow's Hammer" is telling. It also states that some DDIs "failed to impress" at some locations. Such strong language could have easily been avoided but they decided to include it. That's telling. It just doesn't seem like Utah is overly impressed.
Thanks for the link! Lots of good info in there. I think this snippet basically sums up the DDI.
Basically, if the junction acts more like a T (very little through traffic), they work well. Otherwise, they're a bad choice.
Also interesting how many quotes they threw in there. Very philosophical.
(https://www.aaroads.com/forum/proxy.php?request=http%3A%2F%2Fi.imgur.com%2Fs9CkkJP.png&hash=1878277a98691dcbd35a15dd54cc3d8288eb1caf)
Quote from: tradephoric on February 08, 2016, 08:10:25 PM
Quote from: jakeroot on February 08, 2016, 05:38:03 PM
Great map, Trade. Thanks. Looks like some states are more into them than others (looking at you, Utah).
I wonder what Utah has to say about their DDIs? Have they performed any before/after studies?
Thanks Jake. Utah did put together a Guide to Diverging Diamond Interchanges. Here's the opening paragraph of the executive summary:
QuoteReflecting on human tendencies, Abraham Maslow once said, "I suppose it is tempting, if the only tool you have is a hammer, to treat everything as if it were a nail." This maxim, known as Maslow's Hammer, has been frequently observed in science and engineering fields. As new innovations are introduced and applied, they sometimes struggle for initial acceptance but then gain in popularity until they are often over-applied.
.....
Despite this initial success, the DDI is not a one size fits all solution, and it is certainly not the Department's only tool for improving interchanges. Thus, it is important to reiterate that while the DDI has performed very well at some locations, it has failed to impress at others. While it has been a valuable congestion mitigation solution under favorable traffic conditions, it has not fully met expectations in less favorable conditions. Consequently, the DDI may not be appropriate when compared to other interchange types in these less unfavorable circumstances.
http://www.udot.utah.gov/main/uconowner.gf?n=14769524027177477
This doesn't sound like a ringing endorsement for the DDI. The opening paragraph suggests that the DDI is becoming over-applied. The reference to "Maslow's Hammer" is telling. It also states that some DDIs "failed to impress" at some locations. Such strong language could have easily been avoided but they decided to include it. That's telling. It just doesn't seem like Utah is overly impressed.
I read an honest view of DDIs...one that provides a guide where in the future as interchanges will be reconstructed, they can use their experiences to exclude DDIs from consideration at an earlier point. At no point did Utah even come close to saying they weren't overly impressed; they simply learned where DDIs are most beneficial.
QuoteAs new innovations are introduced and applied, they sometimes struggle for initial acceptance but then gain in popularity until they are often over-applied.
That sentence was in the first paragraph of the Utah guide. Keep in mind, there are only 8 DDIs in Utah. They are already suggesting that DDIs are being over-applied when only 8 of them exist in the state (and only 64 exist nationwide). You don't find it a little bit odd they decided to include that sentence?
Do you remember when carpenter jeans were cool back in the 90s? Everyone started wearing carpenter jeans. Then they became uncool. People still wear carpenter jeans... but they are called carpenters. Just like carpenter jeans, DDIs have their place... but it's a niche place. This entire thread questioned if DDIs are a fad. You have Utah, a state that is very familiar with the DDI, eluding that the DDI is a fad and too many are being built in the wrong locations (ie. over-applied).
The most efficient (and cheap) interchange is a cloverleaf, like them or not. Traffic is always moving and they don't require traffic signals. I've been in plenty of cloverleafs and I don't understand the hate for them. Yes, you have to pay attention, but shouldn't you be doing that anyways? I know many truck drivers that say they love cloverleafs, and all of them hate roundabouts.
Quote from: tradephoric on February 09, 2016, 10:30:14 AM
QuoteAs new innovations are introduced and applied, they sometimes struggle for initial acceptance but then gain in popularity until they are often over-applied.
That sentence was in the first paragraph of the Utah guide. Keep in mind, there are only 8 DDIs in Utah. They are already suggesting that DDIs are being over-applied when only 8 of them exist in the state (and only 64 exist nationwide). You don't find it a little bit odd they decided to include that sentence?
Do you remember when carpenter jeans were cool back in the 90s? Everyone started wearing carpenter jeans. Then they became uncool. People still wear carpenter jeans... but they are called carpenters. Just like carpenter jeans, DDIs have their place... but it's a niche place. This entire thread questioned if DDIs are a fad. You have Utah, a state that is very familiar with the DDI, eluding that the DDI is a fad and too many are being built in the wrong locations (ie. over-applied).
I think Utah was pretty clear about when they should be used: if traffic entering/exiting the freeway is heavier than traffic proceeding along the arterial, the DDI should be considered. If through traffic along the arterial is heavier than entering/exiting traffic, the DDI should not be considered.
Seeing as most junctions are designed on a case-by-case basis, I wouldn't call the DDI a "niche" design, so much as a case-specific design (the difference being, niche implies relatively rare, versus case-specific, which implies any number of junctions, just with specific parameters that must be met first).
tl;dr: junctions that act more like T's are a perfect place to build a DDI.
Quote from: US 41 on February 09, 2016, 12:01:00 PM
The most efficient (and cheap) interchange is a cloverleaf, like them or not. Traffic is always moving and they don't require traffic signals. I've been in plenty of cloverleafs and I don't understand the hate for them. Yes, you have to pay attention, but shouldn't you be doing that anyways? I know many truck drivers that say they love cloverleafs, and all of them hate roundabouts.
I'd probably trump that and say a simple diamond is the cheapest...when signals aren't needed (and even when they are). 4 ramps total, all nearly straight, compared to 8 for a cloverleaf. No merge area needed on the minor street, since the ramps can be a T or + with the intersecting road.
Most efficient *and* cheap design though is probably the cloverleaf. Most efficient *but expensive* design is the stack.
Quote from: US 41 on February 09, 2016, 12:01:00 PM
The most efficient (and cheap) interchange is a cloverleaf, like them or not. Traffic is always moving and they don't require traffic signals. I've been in plenty of cloverleafs and I don't understand the hate for them. Yes, you have to pay attention, but shouldn't you be doing that anyways? I know many truck drivers that say they love cloverleafs, and all of them hate roundabouts.
In my non-expert opinion, I'd say cloverleaf interchanges with CD lanes are quite acceptable as freeway-to-freeway interchanges where the volumes of left-turn movements are not too high. But they are problematic when one of the intersecting roads is a non-freeway with sidewalks. The problem is simply that there is no good way to handle crosswalks in a cloverleaf. Three options are: (1) use unprotected crosswalks and hope motorists respect them, (2) spend more in installation and operating costs for signalized crosswalks, or (3) spend a lot more in construction (and potentially maintenance) costs and use elevated sidewalks or pedestrian underpasses. One could argue cloverleaf interchanges with non-freeways present other problems as well, such as inefficient use of land, and stupid drivers stopping on the on-ramps to the non-freeway, but I think the biggest problem is the crosswalks.
Here are a few DDIs that have been "over-applied" :
https://www.google.com/maps/@44.1829417,-92.5767965,543m/data=!3m1!1e3
https://www.google.com/maps/@44.1829417,-92.5767965,543m/data=!3m1!1e3
https://www.google.com/maps/@42.6646009,-83.2393547,1287m/data=!3m1!1e3
https://www.google.com/maps/@35.9830328,-83.6084427,840m/data=!3m1!1e3
These DDIs have very large footprints and a Parclo interchange could have fit. Why build a DDI when you have space to build a Parclo? As previously mentioned, a study found that Parclo interchanges outperform DDIs in nearly every measure of effectiveness and for varying traffic conditions. I recommend reading the study.
Quote from: tradephoric on April 07, 2015, 01:01:29 AM
Here is a comparison analysis of the diverging diamond interchange and partial cloverleaf interchanges:
http://fau.digital.flvc.org/islandora/object/fau%3A3779/datastream/OBJ/view/Comparative_analysis_between_the_diverging_diamond_interchange_and_partial_cloverleaf_interchange_using_microsimulation_modeling.pdf
The Parclo B4 had the shortest delay time and the fewest number of stops for all scenarios tested. In regards to max queue length, the Parclo B4 had the shortest queues in low volume scenarios but the highest queues in high volume scenarios. The explanation for the max queue length of the Parclo B4 is explained on page 92:
QuoteThe maximum queue length on a ParClo B4 occurs at the off-ramps, where cars are trying to enter the crossroad, but are unable to do so since the crossroad is very congested and the vehicles wanting to go through the intersection do not have to stop since they have green throughout the whole cycle length. For the High volume flows, the DDI designs had a much better performance than the ParClo designs.The ParClo A4 had double the queue length than the DDIs, and the ParClo B4 had almost triple the maximum queue lengths at some instances compared to the DDIs.
It's incredibly important to note that the Parclo B4 being analyzed in this study had free-flowing loop ramps. If the off ramps were signalized the max queue of the Parclo B4 would likely be comparable to the other interchanges being analyzed.
The Parclo B4 outperformed the DDI and Parclo A4 in every MOE tested (besides max queue length at high volumes, which can be easily addressed with signalized off-ramps).
Illinois has a DDI now, and at least two others are on the way.
Now open! I-88 at IL59! Will drivers get confused and crash into each other because of the significant thru-traffic on IL59? Find out all this and more tonight at 10!
Two others coming soon:
I-55 at Weber Rd in Romeoville
I-90 at Elmhurst Rd near Mt Prospect/Des Plaines
I think there's gonna be an initial surge in popularity, just because DOT's are going to want to make their stuff look "state-of-the-art" and "progressive," like "ooh, let's try it!" If they turn out to be unhelpful, people will stop suggesting them. But I think they'll just remain as a potential option for diamond interchange redesign, when ROW acquisition potential is limited.
The thing with DDIs is that there isn't much point to using them unless space is limited. There are huge operational advantages over standard diamond interchanges and they're a heck of a lot cheaper than SPUIs while better for pedestrians because of the shorter crossing distances. I'm waiting for NYSDOT to install more.
Quote from: cl94 on February 11, 2016, 04:57:16 PM
The thing with DDIs is that there isn't much point to using them unless space is limited. There are huge operational advantages over standard diamond interchanges and they're a heck of a lot cheaper than SPUIs while better for pedestrians because of the shorter crossing distances. I'm waiting for NYSDOT to install more.
Not to sound too much tradephoric, but DDI's should, really,
only be used if ROW is limited. If it's not, a partial cloverleaf, of some form, likely has much better operating capacity.
Quote from: jakeroot on February 11, 2016, 05:02:44 PM
Quote from: cl94 on February 11, 2016, 04:57:16 PM
The thing with DDIs is that there isn't much point to using them unless space is limited. There are huge operational advantages over standard diamond interchanges and they're a heck of a lot cheaper than SPUIs while better for pedestrians because of the shorter crossing distances. I'm waiting for NYSDOT to install more.
Not to sound too much tradephoric, but DDI's should, really, only be used if ROW is limited. If it's not, a partial cloverleaf, of some form, likely has much better operating capacity.
Precisely. Out east, I see great potential for them because there is rarely room for a partial cloverleaf. I could see quite a few interchanges near me getting the treatment due to the high turn volumes and very tight ROW. The only non-tight ROW scenario it might be good for is where there is little through traffic. In this case, the signals would operate as 2-phase synchronized with through traffic possibly stopping twice.
Since DDIs are being constructed with large footprints that could accomodate Parclos, it's fair to compare the operational performance of each. CL94, I asked you why Canada prefers the Parclo A4 over the B4 and you gave me the following reasons.
Quote from: cl94 on August 06, 2015, 12:28:22 PM
1. Exit ramp is long and straight, providing space for deceleration and reducing the chance of accidents.
2. Turning traffic typically doesn't have to turn cross the path of opposing traffic.
3. All entrances are on the right, providing consistency.
4. Fewer exits from the expressway. Standard is to keep the number of departure points as low as possible.
For each one of your points, strong counter-points can be made that supports the B4 (I listed these counter-points in a previous post...feel free to respond). Secondly, none of your points actually address the operational performance for each type of Parclo. How can you determine what type is Parclo is preferred when you don't know the MOEs for each? If you care about average driver delay, total number of stops, or queue lengths... the Parclo B4 wins.
Quote from: cl94 on August 06, 2015, 12:55:33 PM
There's a balance between delay and cost. Usually, the proposals at any extreme are unacceptable because the balance is not met. You need to be able to sell it to the public. Here, i think the DDI is easier to sell. Hell, being at an MPO, that's a huge part of my job-selling it to the public.
Since both Parclos require similar ROWs, the cost for each should be nearly identical. The focus can shift towards which type of interchange is actually better at moving traffic through it. Can you find any literature that indicates the Parclo A4 is more efficient?
Here is a summary of the results for both balanced and un-balanced traffic conditions.
(https://www.aaroads.com/forum/proxy.php?request=http%3A%2F%2Fi478.photobucket.com%2Falbums%2Frr144%2Ftradephoric%2FTransportation%2520Pictures%2FRandom%2FUntitled3_zpsmyeyojmr.png&hash=fac97d5712dc4455eafda67df91e2eecb1210168)
http://fau.digital.flvc.org/islandora/object/fau%3A3779/datastream/OBJ/view/Comparative_analysis_between_the_diverging_diamond_interchange_and_partial_cloverleaf_interchange_using_microsimulation_modeling.pdf
The ParClo B4 is superior to the ParClo A4 in every simulation tested when analyzing delay time, stop time, and number of stops. Under no circumstance was the A4 better. The only MOE where the ParClo A4 outperformed the ParClo B4 was Max Queue at High 2 & 3. The reason for this is explained in the report:
QuoteThe maximum queue length on a ParClo B4 occurs at the off-ramps, where cars are trying to enter the crossroad, but are unable to do so since the crossroad is very congested and the vehicles wanting to go through the intersection do not have to stop since they have green throughout the whole cycle length. For the High volume flows, the DDI designs had a much better performance than the ParClo designs. The ParClo A4 had double the queue length than the DDIs, and the ParClo B4 had almost triple the maximum queue lengths at some instances compared to the DDIs.
Simply put, if the off-ramp signals of the ParClo B4 were signalized the max queue of the ParClo B4 would be comparable to the other interchange designs tested. And there are many examples of ParClo B4s with signalized off ramps. The ParClo B4 wins out over the Parclo A4 when analyzing common MOEs.
I must play devil's advocate on this thread :bigass:
Saying DDI should only be considered on tight R/W corridors is inaccurate:
1. Take a look at those delay values trade posted. All the DDI values, even the 4 lane geometry, are well within acceptable LOS.
2. It's likely that FHWA approval will be easier to get for four ramps instead of six. If a diamond interchange, for instance, is being upgraded it will take a lower-level report to the feds than adding two ramps.
3. DOT around the country are strapped for cash. Nearly all the parclo variations require more bridge area than DDI.
Also, saying parclo b4 off-ramps can simply be signalized in order to reduce queue isn't fair. What do you think this does to each vehicle's delay? Besides, giving those "left turners " their own lane to accelerate in is one of the parclo b4's best attributes. I'm not saying signalizing them is a bad idea, just that it may diminish the very advantage the geometry has over others.
Quote from: johndoe on February 13, 2016, 06:35:03 PM
I must play devil's advocate on this thread :bigass:
Saying DDI should only be considered on tight R/W corridors is inaccurate:
1. Take a look at those delay values trade posted. All the DDI values, even the 4 lane geometry, are well within acceptable LOS.
2. It's likely that FHWA approval will be easier to get for four ramps instead of six. If a diamond interchange, for instance, is being upgraded it will take a lower-level report to the feds than adding two ramps.
3. DOT around the country are strapped for cash. Nearly all the parclo variations require more bridge area than DDI.
Also, saying parclo b4 off-ramps can simply be signalized in order to reduce queue isn't fair. What do you think this does to each vehicle's delay? Besides, giving those "left turners " their own lane to accelerate in is one of the parclo b4's best attributes. I'm not saying signalizing them is a bad idea, just that it may diminish the very advantage the geometry has over others.
Glad I have someone to back me up. The
main advantage of a DDI is that the bridge can be significantly narrower in most cases (2+ lanes less) and the bridge is
by far the most expensive portion of interchange construction. In the event of an upgrade to an existing diamond, the existing bridge can stay. Good luck doing that with a parclo. I don't know what kind of experience tradephoric has with design and in the field, but from knowing what I do, delay time doesn't mean crap if (a) the LOS remains acceptable and (b) the reduction in delay doesn't offset the increase in cost. Parclos are expensive. DDIs cost no more than a simple diamond, maybe a little less because the bridge can be a lane or two narrower.
Yes cl94, I agree that cost is an important factor to consider but let's get back on point. Previously you said there was a reason Canada prefers the Parclo A4 over the B4. I'm trying to pin you down on why you believe this. The cost for each type of parclo is relatively close (since they require roughly the same ROW and bridge deck widths). While both types of parclos have similar costs, the Parclo B4 is superior when analyzing common measurements of effectiveness under varying traffic conditions (balanced and unbalanced). If two interchanges have similar costs, wouldn't you pick the one that performs better?
I'm not impressed when people talk about how smart they are. It's great that you work in the field... a lot of us do. But citing your resume is not a way to make a compelling argument. Cite a study of your own that supports your side of the argument or at the very least try to poke holes in the study i cited. Do something other than regurgitate how cost is important. I'll ask you again, why does Canada prefer the Parclo A4 over the Parclo B4?
Because they don't like that android in Star Trek: Nemesis
Quote from: johndoe on February 13, 2016, 06:35:03 PMAlso, saying parclo b4 off-ramps can simply be signalized in order to reduce queue isn't fair. What do you think this does to each vehicle's delay? Besides, giving those "left turners " their own lane to accelerate in is one of the parclo b4's best attributes. I'm not saying signalizing them is a bad idea, just that it may diminish the very advantage the geometry has over others.
The reduction in delay at a Parclo B4 is due to the on/off ramp traffic signals only stopping one-direction of travel and they can easily be coordinated to each other (regardless of how close the signals are). It essentially functions as one-way street pair. With a Parclo A4 you have traffic signals that stop both directions of traffic, leading to excess delay because you can't optimize the signal timing for both directions of travel. That's the meat and potatoes as to why the Parclo B4 is superior at reducing driver delay (quite simply, it's easier to time a one-way street than a two-way street). But to your point adding additional on/off ramp signals at a B4 will likely increase total delay. Will the Parclo A4 suddenly have better MOE's though? No way. And there are some major advantages to signalizing the ramps:
1. It makes it easier for pedestrians to cross the street.
2. Off-ramp drivers who need to make a left-turn at an upstream signal don't have to merge and fight their way over into the left-most lane.
3. It reduces the required bridge deck widths (since acceleration lanes are no longer needed).
Consider the following Parclos that service a 6-lane arterial street. The Parclo B4 has double left-turns that extend onto the bridge deck (but since the off-ramps are signalized there are no acceleration/deceleration lanes). Keep in mind that this is a B4 from Florida. Engineers in Florida have to design for extremely long storage lanes because they run incredibly long cycle lengths (since they have long pedestrian crossings along their major corridors). The point is this is a worst case scenario and in other states the left-turns likely wouldn't need to extend onto the bridge deck. OTOH, the Parclo A4 doesn't have any left-turns but it requires acceleration lanes for on-ramp drivers. When comparing the bridge deck widths of both, it turns out the Parclo A4 has a wider deck (even though the A4 doesn't have any pedestrian facilities while the Parclo B4 does). This is an example of how signalizing the off-ramps at the B4 can help reduce the total bridge deck width.
Parclo A4:(https://www.aaroads.com/forum/proxy.php?request=http%3A%2F%2Fi478.photobucket.com%2Falbums%2Frr144%2Ftradephoric%2FTransportation%2520Pictures%2FRandom%2FUntitledA4_zpsup2myon8.png&hash=ac0eefe06e1042e7cb018bc5747e250ff6bfcb74)
https://www.google.com/maps/@41.28607,-96.07538,657m/data=!3m1!1e3
Parclo B4:(https://www.aaroads.com/forum/proxy.php?request=http%3A%2F%2Fi478.photobucket.com%2Falbums%2Frr144%2Ftradephoric%2FTransportation%2520Pictures%2FRandom%2FUntitledB4_zpskk8s1bd1.png&hash=f864236903a44710f97eaf4ccc1cce6af0878047)
https://www.google.com/maps/@26.00754,-80.34041,17z/data=!3m1!1e3
Quote from: cl94 on February 13, 2016, 06:42:42 PMdelay time doesn't mean crap if (a) the LOS remains acceptable and (b) the reduction in delay doesn't offset the increase in cost.
Does delay time mean anything to you if two interchange alternatives cost about the same? If you admit the cost for each type of parclo is similar then you would be forced to look at which performs better. For whatever reason you don't want to do this, so you will probably make some non-convincing arguments why the Parclo A4 is actually cheaper to construct. You said Canada prefers the Parclo A4 over the Parclo B4. All i'm asking is why.
Quote from: tradephoric on February 18, 2016, 02:55:27 PM
Quote from: cl94 on February 13, 2016, 06:42:42 PMdelay time doesn't mean crap if (a) the LOS remains acceptable and (b) the reduction in delay doesn't offset the increase in cost.
Does delay time mean anything to you if two interchange alternatives cost about the same? If you admit the cost for each type of parclo is similar then you would be forced to look at which performs better. For whatever reason you don't want to do this, so you will probably make some non-convincing arguments why the Parclo A4 is actually cheaper to construct. You said Canada prefers the Parclo A4 over the Parclo B4. All i'm asking is why.
You're taking my comment out of context. I never said that in relation to why Canada uses A4s. That particular cost comment relates to why some places use DDIs. I listed what is published online by Canadian agencies and that is all I have. Maybe one of the Canadian members could answer your question. I cannot. All I know is that they avoid them at all costs and their few B4s have significant traffic issues.
^I have been asking you about the operational differences between the Parclo A4 and Parclo B4 for the past few posts. You know that's what I've been asking. Instead you deflected from the question and focused on DDI costs. Let's be clear, the reason your comment is being taken out of context is because you refused to answer my question. Now you finally admit that your previous list of reasons why Canada prefers the Parclo A4 is nothing more than generic talking points you read from some online publication. And yet you still try to discredit the B4 by saying that "the few B4s have significant traffic issues" . A lot of interchanges have significant traffic issues. That's as vague as the "sky is blue" .
Maybe Canada doesn't like exiting loop ramps and think it's a safety concern. I personally feel that point is way overblown. There are literally hundreds upon hundreds of interchanges in North America that have exiting freeway loop ramps. Assuming the results of the study i cited are valid, Canada is willing to double or triple driver delay within an interchange just to avoid a few additional run off the road accidents? If Canada is so concerned with the safety of exiting loop ramps, why don't they eliminate Parclo AB interchanges (which include exiting loop ramps)? There are plenty of those in Canada yet they don't seem to have a problem with them.