Are diverging diamonds a fad?

[jeffandnicole]

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.

[tradephoric]

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.

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.

[Rothman]

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.

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.

I'm sure a study of a single location can be applied universally.

[cl94]

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.

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.

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.

[tradephoric]

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.

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.

[cl94]

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.

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.

[lordsutch]

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.

[jeffandnicole]

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.

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.

[cl94]

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.

[tradephoric]

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? 

[Rothman]

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.

[tradephoric]

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. 

[cl94]

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

[tradephoric]

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.

[cl94]

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?

[tradephoric]

^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.

[cl94]

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.

[vdeane]

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).

[cl94]

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.

[tradephoric]

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? 

[cl94]

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.

[jeffandnicole]

^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.

[cl94]

^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.

[tradephoric]

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.

Well, it sometimes happens .

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. 

[kkt]

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?