If you thought Round-Abouts and Zipper Merges were interesting, wait till you get a load of the NEW type of interchange. This month’s Drivers Ed with Debbie introduces you to the all-new Diverging Diamond Interchange.
They may be a girl’s best friend, but coming soon, folks behind the wheel are going to need Diamond Interchange, and we’re not talking about bling.
Whenever there’s talk about new traffic patterns, there’s bound to be a little push-back. But before you get worried, let’s get a primer on what exactly a DDI is.
I spoke with Wisconsin DOT’s Bill Mohr to get the low-down, “It’s sometimes called a Double Crossover Diamond Interchange. It’s where traffic on the cross street actually moves over to the left-hand side of that road to allow for free left turns basically onto the freeway or onto the main road, which in our case is Interstate 94. And then you have the secondary roadway which is state trunk highway 175 or Brewers Boulevard.”
It’s one of the safer ways of getting on or off a freeway.
Mohr explains, “You’re not crossing in front of traffic for that left turning movement and that’s the safety feature. You’re not making this left turn movement in front of traffic where you could get a t-bone or some sort of other crash.”
Basically, instead of there being two stoplights you have to go through to cross a major freeway, there will only be one. And getting on the freeway should be a breeze without having to cross oncoming traffic.
So this is what you’ll see.
“You will come to an intersection and there will be stop and go lights there. If it’s red, you’ll stop. You’ll see traffic from your right crossing in front of you while you’re stopped. When the light changes to green, you’ll go right through that intersection. If you want to go, say, westbound, you’ll be in the left lane and you’ll just automatically take that lane and go right onto the ramp, right to the freeway. You’re going to see above all the lanes signage saying what lane to be in for what movement you want. If you’re going to want to take the left to go westbound on I-94 it’ll say be in that lane. The right hand movement is exactly the same as a regular diamond interchange,” says Mohr.
Fancy seeing one for yourself? Well, there is one under construction on Brown Deer Road over I-43, but that’s not complete yet. There is one in Janesville at I-39-90 and Wisconsin 26, also known as the Milton Avenue Interchange.
And how do they choose what type of interchange goes where? They’d use this type for any interchange where there’s a heavy left-hand turn movement, but it’s not perfect for every spot.
Mohr says, “What our traffic operations analysis person will do is they look at all different types of interchanges. You have the Diamond, you have the Diverging Diamond, you have a Single Point Urban Interchange, you have free flow ramp interchanges.”
And don’t forget everybody’s favorite, the Round-About.
In the midst of the whole I-94 corridor redo encompassing the area between 16th and 70th streets, not only are they trying to widen the freeway to be better able to handle the heavier traffic volume, but also converting the Stadium Interchange from a full freeway to freeway System Interchange (like the Zoo interchange) to a Service Interchange.
“This interchange, when we’re done, will be more like a service interchange, i.e. a local road with the main line being the interstate,” explains Mohr.
If you’re like me and you do better visualizing it with a picture, check out this video for an example drive through to see how it’s done.
UPDATE: The Brown Deer diverging diamond interchange over I-43 is open as of November 23, 2024! Wisconsin’s Morning News chatted about it, check that conversation out.
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