News:

While the Forum is up and running, there are still thousands of guests (bots). Downtime may occur as a result.
- Alex

Main Menu

Are diverging diamonds a fad?

Started by tradephoric, March 25, 2015, 11:41:26 AM

Previous topic - Next topic

Rothman

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 ;).


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.
Please note: All comments here represent my own personal opinion and do not reflect the official position(s) of NYSDOT.


Ian

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.
UMaine graduate, former PennDOT employee, new SoCal resident.
Youtube l Flickr

NE2

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
pre-1945 Florida route log

I accept and respect your identity as long as it's not dumb shit like "identifying as a vaccinated attack helicopter".

intelati49

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

tradephoric

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.

tradephoric

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.

Ian

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.
UMaine graduate, former PennDOT employee, new SoCal resident.
Youtube l Flickr

tradephoric

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.

Big John

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

mrsman

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.

SignGeek101

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




Mileage Mike

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.

tradephoric

Here's a KMZ file of all known DDI's in America (64 total): 

https://www.mediafire.com/?e5ze6t90ftqgv9h

jakeroot

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?

tradephoric

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. 



jakeroot

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.


jeffandnicole

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.

tradephoric

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).



US 41

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.
Visited States and Provinces:
USA (48)= All of Lower 48
Canada (5)= NB, NS, ON, PEI, QC
Mexico (9)= BCN, BCS, CHIH, COAH, DGO, NL, SON, SIN, TAM

jakeroot

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.

jeffandnicole

#245
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.

Ned Weasel

#246
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.
"I was raised by a cup of coffee." - Strong Bad imitating Homsar

Disclaimer: Views I express are my own and don't reflect any employer or associated entity.

tradephoric

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). 

paulthemapguy

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.
Avatar is the last interesting highway I clinched.
My website! http://www.paulacrossamerica.com Every US highway is on there!
My USA Shield Gallery https://flic.kr/s/aHsmHwJRZk
TM Clinches https://bit.ly/2UwRs4O

National collection status: Every US Route and (fully built) Interstate has a photo now! Just Alaska and Hawaii left!

cl94

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.
Please note: All posts represent my personal opinions and do not represent those of my employer or any of its partner agencies.

Travel Mapping (updated weekly)



Opinions expressed here on belong solely to the poster and do not represent or reflect the opinions or beliefs of AARoads, its creators and/or associates.