Diverging Diamonds

[Midpack]

I much prefer traffic circles over standard intersections, but that’s old news.

Our move to NC has introduced us to diverging diamond interchanges for highway interchanges and overpasses. At first it felt strange and [-]unsafe[/-] counterintuitive. But between the traffic flow and traffic lights, they work very well and reduce accidents by about 50%! There are construction and (less) land benefits too.

I am sure some of you have seen these before. Just interesting and new to us. If I was in a community proposing DD’s, I’d support it!

https://www.divergingdiamondinterchange.org/

The Diverging Diamond is based on the idea that if you can eliminate the need for left-turn arrows, then signals will have maximum efficiency, fewer conflict points, and be able to serve more traffic with better safety and less congestion.

Mr. Don Saiko, MoDOT Project Manager, reports that in survey's conducted after opening, 97% of respondents believe the projects made the area seem safer, 95% believe it is less congested, and 87% believe it is easier to drive than it was before. Mr. Saiko also notes that crash data collected in the first six months suggest a 50% overall reduction.

Fear that drivers would be confused and make mistakes in moving to the "wrong side of the road" have proven unfounded. Having driven this one in Utah, good channeling and signage make the transition very natural. You can hardly tell that anything unusual is happening. Hooray that DOTs across the country are finally taking this concept seriously!

 

[cooch96]

I’m in the construction business. I’ve only picked up traffic engineering tangentially, but I’ve noticed improvement in traffic designs: SPUIs, diverging diamonds, double roundAbout (which I know are common in Europe), have done a decent job of increasing road capacity and serviceability to keep pace with the increased traffic density. It makes me wonder how much useful innovation is out there and on the drawing boards.

What kills me is how long it takes to get the simple things improved, like light timing and flashing amber left-turn signals. It baffles me why those things weren’t optimized in the 70s-90s.

 

[pb4uski]

We recently had a diverging diamond completed about a year ago at one of the busiest interstate intersections in Sarasota. Many were skeptical, but now most people concede that it works very well. The video has some cool views of what it is like to drive it.

 

[Winemaker]

We had one built in Washington PA, and I believe it works great.

 

[Ronstar]

As a driver, I like diverging diamonds. I know of only 3 in the Chicago area. Illinois route 59 at I-88, Elmhurst Road at I90, and a new one under construction at Weber Road at I55. I expected confusion navigating through a DD, but I hardly notice anything different. Less traffic signals is a good thing.

 

[LRDave]

Two of the most congested interchanges in Metro Atlanta were converted to diverging diamonds and I think it helps traffic some and flows pretty well. It is not as shocking to change sides of the road as you might think it would be.

The traffic around these two intersections is still hellish and should be avoided if at all possible.

 

[Midpack]

What kills me is how long it takes to get the simple things improved, like light timing and flashing amber left-turn signals. It baffles me why those things weren’t optimized in the 70s-90s.

+1. I went to high school in Europe where traffic circles were everywhere. It seems like it’s taken 40-50 years to come to the US with a few exceptions and they’re still not very common.

I read diverging diamonds have been around for 20 years but I’d never seen or heard of them until this year! If they reduce accidents by 50% and use less land, why aren’t they more common?

 

[Potstickers]

We have one in the next town over. It took me about 10 trips through it before the panic of "I'm driving on the wrong side of the road" abated.

It seems to work fine and does seem to reduce the clogs that often happened at that intersection.

 

[cooch96]

+1. I went to high school in Europe where traffic circles were everywhere. It seems like it’s taken 40-50 years to come to the US with a few exceptions.

I read diverging diamonds have been around for 20 years but I’d never seen or heard of them until this year! If they reduce accidents by 50% and use less land, why aren’t they more common?

I can’t speak for every DOT and every project obviously, but there are two big reasons. Civil engineers are probably he most conservative engineers, and for good reason. Also, the process of road construction is frequently a very long process: traffic study, design, environmental impact study, permitting, and then funding routinely takes over a decade. So projects getting built today were possibly (likely) designed when DD’s where a new and unproven concept.

 

[Marc]

I recently moved to Texas where there are an ever increasing number of diverging diamonds. Although I think they work well, they still suffer from multitude of red light runners that make the intersections more dangerous than they should be. I am a big fan of roundabouts and double roundabouts and wish they became more common in USA.

Marc

 

[Chuckanut]

When I first was in New Jersey I was introduced to 'Jug Handles' for left turns.

To make a left turn one stayed in the right lane, and drove past the street one wishes to turn left onto. On the right is an exit that curves around and merges with the street you want to run left on, but a bit ahead of the intersection. You simply drive straight through the intersection and you are now going 'leftward' on the street you want to be on. They seemed to work very well.

The standard left turn light is horrible by comparison. Years ago UPS figured out that eliminating left turns was a far more efficient way to get around a city.

https://theconversation.com/why-ups-drivers-dont-turn-left-and-you-probably-shouldnt-either-71432

UPS have moved away from trying to find the shortest route and now look at other criteria to optimise the journey. One of their methods is to try and avoid turning through oncoming traffic at a junction. Although this might be going in the opposite direction of the final destination, it reduces the chances of an accident and cuts delays caused by waiting for a gap in the traffic, which would also waste fuel.

 

[pb4uski]

...I am a big fan of roundabouts and double roundabouts and wish they became more common in USA.

Marc

I also like roundabouts.... I prefer single to double but the double are ok.

 

[Blueskies123]

+1. I went to high school in Europe where traffic circles were everywhere. It seems like it’s taken 40-50 years to come to the US with a few exceptions and they’re still not very common.

I read diverging diamonds have been around for 20 years but I’d never seen or heard of them until this year! If they reduce accidents by 50% and use less land, why aren’t they more common?

I lived in the UK for 3 (long) years. I loved roundabouts once I got used to them but I noticed in very large roundabouts with lots of roads and traffic they can be a bit much. I think the diamonds make sense for large express way intersections while round about make sense for smaller interchanges.

 

[Midpack]

I lived in the UK for 3 (long) years. I loved roundabouts once I got used to them but I noticed in very large roundabouts with lots of roads and traffic they can be a bit much. I think the diamonds make sense for large express way intersections while round about make sense for smaller interchanges.

I don’t think they’re meant to be alternatives, apples and oranges. Traffic circles are for flat intersections while diverging diamonds are for highway interchanges with bridges.

 

[SecondCor521]

We have something similar but different in my home town. It's affectionately called the "Flying Y":

http://what3words.com/nasal.nights.mouse

 

[GalaxyBoy]

We have one and I think it’s great. Locals here don’t handle change well and I hear things like, “it’s so confusing,” “dumbest idea ever,” and “there are so many accidents there” (there aren’t). Eventually it will catch on.

We’re getting a fair number of roundabouts too. I’ve witnessed people stopping in the circle at each exit, one by one. The newspaper noted after the first one was installed that the neighbors were complaining about the noise from horns honking. One near me has two lanes around half of it. You take your life in your hands if you believe everyone will follow the painted lines.

 

[Midpack]

We’re getting a fair number of roundabouts too. I’ve witnessed people stopping in the circle at each exit, one by one. The newspaper noted after the first one was installed that the neighbors were complaining about the noise from horns honking. One near me has two lanes around half of it. You take your life in your hands if you believe everyone will follow the painted lines.

+1. The first roundabout in my former hometown was a circus for about two weeks, not promising. Lots of horns, drivers afraid to enter at all, other drivers in the circle stopping at every exit, missing exits and going around more than once, etc. But locals began to catch on quickly after that, frankly I was proud of my fellow townsfolk. And they took subsequent roundabouts (up to six I can remember) in stride easily. It’s rare to see someone get confused (likely out of towners) but I’m sure everyone everywhere will take them in stride eventually - just like Europe.

Same with diverging diamonds. Looks like a bad idea the first time you’re confronted with it, but actually a great idea that’s easy to get used to. Traffic signals make it very hard to mess up, newbies (self included) don’t realize that immediately.

 

[SecretlyFI]

I’d never seen or heard of diverging diamonds before today. I think it’s genius. I watched the video posted above from Florida and it seems to make perfect sense.
As always, learn something every day on this forum! And this, on the same day I saved a bundle using Zenni optical. Thank you e-r.org!

 

[aaronc879]

We had one installed in my town last year. It eliminates left turns which reduces accidents. When I first saw the diagrams I thought people would go the wrong way but I have not heard of any issues at all and it's been a full year now.

 

[braumeister]

I’d never seen or heard of diverging diamonds before today.

Same here. I'm a big fan of modern roundabouts, jug handles, and flashing yellow left arrows, but this is a new one on me. Looking forward to encountering one before long.

 

[Just_Steve]

I’d never seen or heard of diverging diamonds before today. I think it’s genius. I watched the video posted above from Florida and it seems to make perfect sense.
As always, learn something every day on this forum! And this, on the same day I saved a bundle using Zenni optical. Thank you e-r.org!

Yup, +1

 

[camfused]

Midpack, if you haven't seen Biffa on YouTube use Cities Skylines, I think you will like it! Example:

 

[pb4uski]

^^^^ Now, a clockwise roundabout, that would certainly make things interesting!

 

[braumeister]

^^^^ Now, a clockwise roundabout, that would certainly make things interesting!

Haven't been to the UK lately, eh?

 

[camfused]

^^^^^ In the US, yes. On the other hand, when I see people in the roundabouts at the local shopping center, it probably wouldn't make any difference. Sad.