Diverging Diamond Interchanges

[UberXY]

Have you guys experienced one of these yet? Our state is building one about 15 miles from me, near a large Walmart distribution center where hundreds of trucks daily exit an interstate for a short drive to the depot.

 

 

It's a little confusing because you cross a bridge where the lanes are reversed - you are driving on the left hand side of a four lane road. It makes sense in the long run, but if you first encountered one of these at night in the rain, it might be a little confusing. To their credit, there is an unusual amount of signage and lane painting.

 

Explanation:

 

Diverging Diamond Intersections

[eddd]

They completed one recently in St. George, UT. I've used it several times and find that it is a very useful design. Traffic definite flows more smoothly and with way less bottle necks.

[tkrandall]

There is one here in metro Atlanta on I-285 at Perimeter mall. Works great. More are on the way....

 

http://www.gwinnettcounty.com/portal/gwinnett/Departments/Transportation/DivergingDiamondInterchanges

 

http://portal.cobbcountyga.gov/index.php?option=com_content&view=article&id=1273:dot-diverging-diamond-interchange-at-wade-green&catid=153:department-of-transportation&Itemid=298

 

 

[Mrs. Caddis]

They are starting to construct one in the next week or so in Louisville Co at the intersection of Rte 36 and McCaslin Blvd. It seems like it will be a bit confusing at first but the left turns onto Rte 36 are a major pain right now. Seems to be the solution for where there is not enough land left to build a full cloverleaf.

[elkroeger]

Hey, now those are neat! Apparently they're safer, more efficient, and cost a lot less to build....

 

Watch the

of travelling through the interchange. Seems pretty intuitive to me.

[DaveTheAffable]

Wow... I had never seen or heard of this. Very cool.

 

Found this slow moving EXCELLENT animation. The slow aspect was important for me...lol. It took me a couple minutes to "get it".

 

[Selden]

Two of these have been finished in the Atlanta metro area in the past year. Although they take some getting used to, diverging diamond traffic exchanges definitely speed up traffic flow — I was quite surprised at the improvement on both (I-285 & Ashford-Dunwoody, and I-85 & Pleasant Hill).

[Gundecker]

It seems we are getting one built near me! I will use it on my way to and from work. It's is where and interstate ( I 10 & I110) it's little brother cross. In addition there are service roads on three corners of it from what I can gather. My little town is changing. Of course there is also a Walmart nearby..... Sigh.

[Fubar]

I hope we don't get them here, people have too much trouble with a simple traffic circle, if you consider a traffic circle with extraneous right turn lanes simple.

[eddd]

I hope we don't get them here, people have too much trouble with a simple traffic circle, if you consider a traffic circle with extraneous right turn lanes simple.

 

The traffic circles are a whole other thing and can be confusing for many especially when there is one on each side of an expressway intersection.

 

I had no difficulty immediately adapting to the Diamond Interchange, and I haven't seen any others with issues. It might look confusing, but using it isn't confusing at all. With the marking, signals, and barriers you have to try really hard to go the wrong direction.

[greiffster]

I'm with Fubar on this. I've done design work on both the classic cloverleafs as well as the diamonds. The cloverleafs allow for the greatest volume but also require the most R.O.W. Less R.O.W. is how you get to the diamond concept. But now you have lights which means traffic is stopped, and capacity is decreased. But it's mostly intuitive. You get to the end of the ramp, you see the light, and you go left or right.

 

The diverging diamond requires about the same R.O.W. as a regular diamond and can allow more volume depending on flow in all the different directions. But, to the average driver, counter-intuitive. You are asking drivers to veer left of opposing traffic. You can sign this thing to kingdom come, but it's a complex traffic pattern. Complex traffic patters mean confusion to drivers which results in accidents. I haven't seen any numbers on these things, but I hope the increased volume is worth the potential confusion.

 

Roadway design is the study of the painfully obvious. The merely obvious is no longer enough as you factor in all of the distractions plaguing today's drivers.

[russell_bynum]

You can sign this thing to kingdom come, but it's a complex traffic pattern. Complex traffic patters mean confusion to drivers which results in accidents. I haven't seen any numbers on these things, but I hope the increased volume is worth the potential confusion.

 

I read somewhere that increased confusion results in fewer accidents because people slow down because they don't know WTF they're supposed to do. It's "Wow...this is really screwed up...where the hell am I supposed to go? I'd better be careful." rather than the usual "Ho hum...just another intersec OH SH*T!!! CRASH!!!!!"

[greiffster]

I read somewhere that increased confusion results in fewer accidents because people slow down because they don't know WTF they're supposed to do.

 

I'm sure there is some truth to that.

 

The original DDI designers claim the intersection to be safer because it reduces the number of conflicts. Specifically the number left turns across oncoming traffic, statistically the most dangerous. I hope it is.

[Fubar]

I hope we don't get them here, people have too much trouble with a simple traffic circle, if you consider a traffic circle with extraneous right turn lanes simple.

 

The traffic circles are a whole other thing and can be confusing for many especially when there is one on each side of an expressway intersection.

 

I had no difficulty immediately adapting to the Diamond Interchange, and I haven't seen any others with issues. It might look confusing, but using it isn't confusing at all. With the marking, signals, and barriers you have to try really hard to go the wrong direction.

There is one, two lane road in town that I get to use all the time as my son's school is on it. They have 7 circles on it currently (one has a turn lane(!) that messes up everybody & one has an alternate route that must yield and causes so many issues) and they are adding one more. There will only be two traffic lights in about 4 miles of roadway, where it crosses 4 & 6 lane roads.

 

Additionally, I just heard rumor that we are getting a 2X or double diamond at an increasingly "cluster of firetrucks" interchange, specifically where it goes under I-75 (exit 213).

Currently, my complaint with it is revolves around turning left from the northbound off-ramp. Two lanes turn left (and two or three right) and since most cagers are lazy a$$holes(!), they turn into the two left turn lanes that will put them back onto the interstate southbound. I take my appropriate lane only to get squeezed by Joe or Jane Dipstick who suddenly realizes what a foolish thing they have done as they brake - eating the space I left between us - and slide to the right to get into the westbound lane. Since there is already someone to my right, in their appropriate lane, this is a pucker-inducing moment nearly every time. It doesn't matter whether the trip is on two wheels or four, it happens every time I'm not in front.

Sadly, I really don't have another, viable, route available. And with the new mall opening at the light just a few hundred feet to the west this fall - just as the snowbirds come back! - this is going to be collision central unless FDOT does something RTF NOW!

[enfoman]

I have not noticed that particular type of intersection around me. I will have to study it more to grasp it. The latest and greatest and going very well for the last two years I would say is an intersection called a SPUI- Single point urban interchange. It is at the confluence of Route US2 and interstate 87 outside of Albany NY. Just as the name says, All traffic comes to a single point and flows pretty good. That double diamond seems to take it to a similar idea times 2.

 

SPUI---- in action////

 

 

 

 

 

 

[Glenn Reed]

I have not noticed that particular type of intersection around me. I will have to study it more to grasp it. The latest and greatest and going very well for the last two years I would say is an intersection called a SPUI- Single point urban interchange. It is at the confluence of Route US2 and interstate 87 outside of Albany NY. Just as the name says, All traffic comes to a single point and flows pretty good. That double diamond seems to take it to a similar idea times 2.

 

We have one of these at a particular interchange between a surface road and our Beltway. It does seem to work well, but was a little weird at first.

[UberXY]

I've been using this intersection now for a few weeks, and it's pretty convenient. One bit of caution: if you are following someone who is unfamiliar with the concept, they may exhibit undesirable behavior, like slowing down to 5 mph, hesitating, or suddenly stopping where stopping isn't required. If I am following someone with out of state plates, or perhaps a very senior citizen, I give them a lot of extra room and anticipate some confusion.

[szurszewski]

You can sign this thing to kingdom come, but it's a complex traffic pattern. Complex traffic patters mean confusion to drivers which results in accidents. I haven't seen any numbers on these things, but I hope the increased volume is worth the potential confusion.

 

I read somewhere that increased confusion results in fewer accidents because people slow down because they don't know WTF they're supposed to do. It's "Wow...this is really screwed up...where the hell am I supposed to go? I'd better be careful." rather than the usual "Ho hum...just another intersec OH SH*T!!! CRASH!!!!!"

 

There is literature available on this - I'm purusing while eating breakfast this morning, so no time for references, but I could dig some up if anyone is interested. In the Netherlands, starting a couple/few decades ago, they started configuring the points where main highways/routes passed through small villages by basically getting rid of almost all traffic controls, reducing the sidewalk curb heights, putting everyone closer together and basically making it seem more like you were driving through the center of a park than an intersection. It was very effective at reducing crashes and injuries basically becauase it made eveyone have to slow down and pay attention (which I suppose could also be said by saying it confused everyone, but I'm not sure that's exactly the right phrase). Pretty fascinating stuff.

[Joe Frickin' Friday]

There is literature available on this - I'm purusing while eating breakfast this morning, so no time for references, but I could dig some up if anyone is interested. In the Netherlands, starting a couple/few decades ago, they started configuring the points where main highways/routes passed through small villages by basically getting rid of almost all traffic controls, reducing the sidewalk curb heights, putting everyone closer together and basically making it seem more like you were driving through the center of a park than an intersection. It was very effective at reducing crashes and injuries basically becauase it made eveyone have to slow down and pay attention (which I suppose could also be said by saying it confused everyone, but I'm not sure that's exactly the right phrase). Pretty fascinating stuff.

 

Traffic Calming

[greiffster]

Traffic Calming

 

Most of the "new" interchange designs in the US are equally about safety as they are traffic capacity, probably leaning a bit toward the latter. Kind of the opposite as it relates to calming and slowing traffic down. It's actually very difficult for DOTs on state routes to reduce design speeds (and subsequent statutory and posted limits) because it reduces traffic capacity. We are trying everything to squeeze more and more traffic through the same arterials and intersections without any additional delays. It's the 10lbs. of crap in a 5lb. bag problem.

[Fubar]

It's actually very difficult for DOTs on state routes to reduce design speeds (and subsequent statutory and posted limits) because it reduces traffic capacity. We are trying everything to squeeze more and more traffic through the same arterials and intersections without any additional delays.

Have you ever heard of one increasing the speed limit anywhere? Not around here, for sure.

[eddd]

Have you ever heard of one increasing the speed limit anywhere? Not around here, for sure.

 

In the wide open spaces of Texas and Utah there have been increases. In Utah they raised it to 80 on sections of the Interstate. In Texas it went to 80 on sections of the interstate and 85 on a toll road near Austin. It also went up on rural highways to 75 or maybe 80.

[greiffster]

Have you ever heard of one increasing the speed limit anywhere? Not around here, for sure.

 

No, not usually, and that's also the problem. People want to get places quicker with less traffic. They also want slower speeds, especially where they live. And people live everywhere. Lower design speeds = less traffic capacity.