Thursday, April 12, 2018

A "diverging diamond" interchange?


I'd never heard of them, until Wirecutter posted this video report.





Has anyone driven through them?  Are they as good as they're claimed to be?  Please let us know in Comments.

Peter

23 comments:

The Raving Prophet said...

There's a few near me. They do cut down on congestion. People coming off or getting on the interstate are able to do so without having to wait at a stoplight (most of the time). It takes a little getting used to, but once you know what's going on it really is good for interchanges that see too much volume for even a single point intersection to be effective.

Ted said...

There's at least one in a town near me. I haven't used it often, and it does kind of confuse you at first (it's well marked, but kind of wth?), but it definitely works.

JLM said...

We have one here in Anchorage (google:Glenn highway/Muldoon interchange) and while it was VERY ODD at first, it really is much quicker to navigate than before. Now if someone could teach these people how to drive properly, that would be even better!
(grumble grumble, mutter mutter)

Larry said...

I think they'd work even better if there were two overpasses built into it so traffic wouldn't have to stop at all, but that would be a lot more ecpensive to build. It does like like an improvement on the usual type, and especially some of the abortions I've run into over the years.

Dwan Seicheine said...

The problem with them is that EVERYONE must know how to use them. All it takes is one idiot who doesn't and then it's pileup time.

McChuck said...

There's one at US-15 and I-66 in Virginia. It works pretty well. The normal traffic jams and slowdowns have more or less disappeared. It feels really weird the first time you drive through it, though.

http://www.virginiadot.org/projects/northernvirginia/i-66_and_route_15_interchange.asp

Rev. Paul said...

I was going to mention the Muldoon overpass, but JLM beat me to it.

Jonathan H said...

I've been through a couple of them - they are really weird, but not bad once you get used to them. My biggest problem is that they confuse people who haven't seen them before; I don't think they should be in an area that gets lots of tourists.

Kamas Kirian said...

Yes, there's one in Moorhead that opened a year or two ago. And there's one coming this summer down the street from me in West Fargo. They take a little getting used to, as it seems backwards, but it actually seems to flow quite quickly. It would be nice if they didn't suddenly add a lane for turning back at the entrance to it without marking it as a lane that "must" turn.

Tony Tsquared said...

They have been converting overpasses in NE Atlanta for the past few years. Before it would take as long as a half hour to negotiate getting across the interstate or on or off the interstate. Now it is never more than 5 minutes.

Will said...

If it's a critical intersection, that you have enough space to build all that road surface, it would make sense to elevate one side of that crossover. Eliminating crossing traffic would really keep things moving, and dramatically decrease the costs of accidents/injuries/deaths in that area.
I would still keep that same offset, instead of stacking the road sections, in any location that might be subject to earthquakes. I don't think adding the elevation would significantly increase the cost compared to the total outlay for all that construction, but, I'm not a road engineer.

Dave said...

They're building one here in College Station, intersection of FM 2818 and Raymond Stotzer PW.

What's going to be interesting is Stotzer to 2818 is a major route from the Northgate bar district to an area with a large number of student apartments. Watching the inebriated try to sort this thing will be, erm, interesting for those of use who drive black and white cars with lights on top.

Jon said...

They've built a few in the towns surrounding Austin. They have helped quite a bit, but do take some getting used to.

Mad Jack said...

I've driven through a few. The design helps, but it works best if the drivers involved know what they're doing, and I don't just mean through the interchange. If the drivers are experienced, safe drivers, then it works. Just let some asshat get creamed while using his cell phone, and the whole show ties up for hours while officialdom clears the half-dozen or so poor schmucks that said asshat took with him when he wiped out.

quizikle said...

They're OK as long as you're not in a "Drat, this isn't my exit" place. They're really hard to get back on from (re: US15/I64)
Q

645645645645645 said...

I use one every couple of days. Easy to use and they really work.

Contrarian View said...

They put one in at Zion Crossroads in Virginia about three years ago. It works great.

Richard Douglas said...

They are a much better idea than the "let's Europeanize American Roads" traffic circles that were built undersized for semi-tractor trailers that US DOT shoved down our throats the last few years. I have driven through several in Wisconsin and Illinois, and they are easy to negotiate if you know what is going on. I agree that they are difficult to recover from a direction on, and can be somewhat confusing for the first few times...you do wind up driving on the English side of the road for a bit. Elevating the traffic is done on higher volume interchanges, eliminating the need for the double diamond, but that leads to the wedding cake multi-level interchanges like in Salt Lake or Las Angeles and adds exponentially to the expense.

Odysseus said...

They help with some problems like gridlock, and I find them less stressful than the current roundabout construction fad.

Aesop said...

Pros: cheaper construction, because no overpasses/underpasses.

Cons:
You now have 8 opportunities for merge crashes, and two opportunities for head-on collisions, with no way for cross traffic to cross at all.

This is therefore a genius idea, if the mean standard intelligence is autism or mental retardation.

For average IQs, cloverleafs cost more, but work better, provided the nitwits in charge of construction build enough lanes to handle the capacity of traffic actually using them.

If they don't do that, it doesn't matter what they build, because physics and economics are real:
You can't fit 10 pounds of crap in a 5 pound bag, nor thereby get it for half-price.

If you want better drivers, the place to screen them out is not the interchange, it's the DMV counter: make the tests too hard for morons to pass, make the practical tests annual, lower the accident points threshold to trigger a mandatory suspension, revoke anyone's license who fails either portion and give them a bus pass, with a mandatory one-year wait for re-test, and anyone caught driving without a license gets six months on a chain gang, picking up trash and filling in potholes in the lanes next to traffic. Just like they do for DUIs.

Idiotic roundabouts only work in Europe because many of those nations make getting a driver's license about as easy as getting a private pilot's license. And they still drive like maniacs, as any visitor to Italy could tell you.

LCB said...

Here in Butler County, Ohio, on By-Pass 4, we have these "things" that are supposed to improve traffic, but for the life of me I can't see the benefit. When you pull up to BP 4 at a light, and wish to go left, you are stopped by a light and then have to turn right. Immediately after turning right, you queue up at another light, which allows you to do a U-turn and then proceed in the left direction you wished to travel on. The only thing it seems to prevent is just crossing straight through an intersection. But you still have the chance of getting hit from either direction if someone runs a light, although now the two directions you can get hit from are controlled by two different lights. I have no idea what these are called or I'd look it up to give you all a link.

D.J. said...

There's one a bit north of Austin on I-35 at the Ikea exit. Flow over the freeway is better now, but it is very odd driving on the left side going over that overpass.

Mark Jewell said...

There is one at US93/95 and Horizon Drive in Henderson, NV. It has both traffic lanes and bike lanes. People were put off by it at first, but they quickly adapted. So far I have not heard of any major issues. No word on if they plan on putting in any more in the Las Vegas area anytime soon.