Diverging diamond interchanges: how prevalent across US?

[smccutchan1]

In the last five years, UDOT (Utah Department of Transportation) has installed several "diverging diamond" interchanges. These have been primarily along either Bangerter Highway which is a limited access expressway that has signalized intersections every couple of miles or as part of the very large reconstruction of Interstate 15 through Utah County. Utah County is the southern part of the Salt Lake City metropolitan area.

I have had the opportunity(?) to navigate a few diverging diamonds and, while I see the efficiency of them, are not sure whether diverting the traffic from one side of the road to the other and back again in a space of a couple of hundred feet is actually that big of a deal and worth the effort. From my experience you don't want to follow a senior citizen driving a big Buick through a diverging diamond unless you enjoy watching the elderly freak out behind the wheel.

How prevalent are these across the US? What's been your experience?

If you are unfamiliar with what a diverging diamond is, click on the following link to a report prepared for UDOT about the Utah County 1-15 reconstruction called CORE.

http://www.udot.utah.gov/main/uconow...72614219775523

[Brocktoon]

That is all we have in Arizona. Very few clover leafs in this area but land is plentiful can was cheap.

[rcgplanner]

It would be intersting to see what the cost difference is between a traditional interchange and a DDI. I can see how they could reduce traffic congrestion at busy interchanges but is it it that big of an improvement over a protected green light? I know MODOT was the pioneer on this new interchange back in 2009,it will be interesting to see FHWA studies on what improvement DDI's actually bring.

[DetroitPlanner]

I know we don't have any in metro Detroit and it stands to reason that there are none anywhere in Michigan. Odd buggers. I still take them over the U-turn traffic signal phases I've seen in Orange County CA!

[Bubba]

The only DDI in Georgia that I'm aware of was put in place at the Ashford Dunwoody Road interchange with I-285 about a year ago - Mrs. Bubba's office building is near that interchange. From what I've heard from her (and my limited experience with that DDI), all it's done is move the usual traffic back-up off of the bridge over I-285 back onto Ashford Dunwoody Road, and made it a lot more difficult for her to get out of building and onto the road in the afternoons (and it doesn't seem to make getting from one side of the bridge to the other (or onto the interstate) any faster or easier).

Meh.

[dvdneal]

I know AZ had lots of diamonds, and when I was there my city talked about building a DDI interchange, but we didn't have one yet. I'm not sure if it's still in the plan, but we thought all the retirees would go nuts driving on the wrong side of the road. Although it does seem to move traffic through faster.

Here in soviet Kansas we use cloverleaf as efficient model of freeway interchange.

[mgk920]

I'm open to the idea of using them and they do have several of advantages, including not having left turning vehicles interfering with each other. I also like the fact that a DDI can be retrofitted on a traditional diamond at minimal cost (no major bridge re-engineering is needed) and that they are scalable - you can add lanes to the street without greatly affecting their performance. OTOH, I do worry about what might happen if/when the power fails and the signals go dark.

WisDOT is studying DDIs and is also currently actively using roundabouts at new and rebuilt freeway interchanges. The roundabouts that they have installed on diamond interchanges on US(I)-41 in the Neenah and Oshkosh, WI areas appear to be performing very well.

I do like the fact that roundabouts continue working just fine when the power goes out.

Mike

[ursus]

I know we don't have any in metro Detroit and it stands to reason that there are none anywhere in Michigan. Odd buggers. I still take them over the U-turn traffic signal phases I've seen in Orange County CA!

UDOT is trying the pass-through U turn in place of a left turn onto the interchange as well. I don't know what you call those. Is that what you're referencing here?

[anthrus]

I have been in one! My home town of Rochester, NY installed a divergent diamond last summer in one of its suburbs, Brighton. At the time, it was only the sixth in the world.

From my experience, it seems like it is working. The divergent diamond is near an industrial area, and trucks would often back up onto the adjacent interstate waiting to get off. I have only taken that exit a few times since, but I have never noticed that problem. That said, I suspect the Genesee Transportation Council, the area MPO, has way better data than your humble, uneducated data point.

[Suburb Repairman]

maybe Random Traffic Guy has seen one, but I haven't seen a DDI in Texas yet nor have I encountered one personally. I understand one is being considered in Austin/Round Rock on I-35, but haven't seen any details on it yet.

[DetroitPlanner]

UDOT is trying the pass-through U turn in place of a left turn onto the interchange as well. I don't know what you call those. Is that what you're referencing here?

Most of the arterials in Orange County have a very narrow median running down the center. In order to access a SB property when going NB you need to make a U-turn in the next major intersection. It is a protected turn that is a separate phase. In Michigan we employ Michigan lefts and center turn lanes to achieve these movements.

[Random Traffic Guy]

maybe Random Traffic Guy has seen one, but I haven't seen a DDI in Texas yet nor have I encountered one personally. I understand one is being considered in Austin/Round Rock on I-35, but haven't seen any details on it yet.

None that I know of constructed. I think they might be looking at one for the new Nebraska Furniture Mart in The Colony.

DFW-area hasn't been kind to alternate interchange styles lately. Apparently the Michigan-left-turn setup at Legacy and Preston in Plano is going to be changed... to what, I don't know.

[illinoisplanner]

Work is set to begin soon on constructing Illinois' first diverging diamond interchange at I-88 & Route 59 in Naperville. Work is set to begin next year and will probably be finished in 2015 or 2016. It is currently a traditional interchange that is very busy, so it should be interesting to see what happens when they convert it. I'll let you know how it goes!

[CanadaJimmy]

This is why I come to this forum - saw this mentioned in another topic by DetroitPlanner - incredibly exciting and a very smart solution to a problem! Found a good explanatory video on DDIs also:


I've not seen any where I live, but I could imagine them really helping smooth out traffic flow. I mentioned it to one of the driving advocacy groups around here but they didn't seem as impressed, remarking that some drivers here struggle enough with roundabouts. I personally think that can't be that complicated, just follow the arrows...

[BooDog]

The main idea of a Diverging Diamond Interchange is safety, not reduction of congestion. The elimination of left hand turns will (in theory) reduce accidents.

This type of intersection is actually patented, along with other types of intersections. Here is the DDI patent: https://www.google.com/patents/US5049000

Excellent article on comparing/contrasting different intersection styles, including DDI: http://www.westernite.org/awards/bes...Siromaskul.pdf