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The 'diverging diamond interchange' may come soon to a busy intersection near you


If you're sitting in a car, waiting and waiting and waiting to make a left turn, well, this next story is for you. Imagine an intersection where turning left is just as easy as going straight. This innovative design already exists and may be coming soon to a traffic-clogged intersection near you. NPR's Joel Rose reports.

JOEL ROSE, BYLINE: As you first pull into the intersection, you may notice that you're crossing over to the wrong side of the road.

GILBERT CHLEWICKI: There were - a lot of people looked at me like I was a little nuts. Like, why are you putting me on the other side of the road?

ROSE: This is Gilbert Chlewicki. He is the inventor of the diverging diamond interchange, as it's known because of how it looks from above. He met me at one of these intersections in northern Virginia, wearing a neon yellow vest for safety.

CHLEWICKI: Fifteen northbound and 15 southbound cross each other so that over the bridge, you're actually driving left side of the road.

ROSE: Here's how it works. The right and left sides of the road cross over each other at a stoplight. Once you're on the left side of the road, left turns are easy because there's no oncoming traffic in the way. Instead of waiting for a special signal, you get a free left turn. That makes these interchanges faster and safer. There are now more than 200 intersections like this in the U.S. But at first, Chlewicki says, it wasn't easy to convince traffic engineers.

CHLEWICKI: Anything different is a hard sell.

ROSE: So, like, what did you hear? What did people say they were concerned about?

CHLEWICKI: Safety was the big question. Will this be safe?

STACY REESE: Part of the thought was, OK, we put it in there. We see how this works. Let's try it. Let's see. We were willing to take that risk.

ROSE: Stacy Reese is with the Department of Transportation in Missouri, the first state to try the diverging diamond design back in 2009 at a notoriously backed-up intersection in Springfield, where it could often take as long as 20 minutes to make a left turn. When MoDOT opened the new intersection, those backups cleared up immediately, and Reese says there was another benefit. It was safer than the traditional intersection it replaced.

REESE: We did see the crashes reduced somewhere in that 40 to 50% range pretty much, you know, instantaneously.

ROSE: Left turns are a big problem everywhere. They have a lot of what traffic engineers call conflict points with pedestrians and with other cars. The diverging diamond design eliminates some of those conflicts and dramatically lowers the risk of side impact, or T-bone, crashes, which tend to be especially deadly. Still, some drivers are hesitant, like Logan Wilcox, who drives a school bus near a double diamond intersection in Virginia.

LOGAN WILCOX: I hate it. I feel like someone else that's not familiar with it is going to be coming through, and they're going to struggle with it. It makes me, like, really concerned that someone's just going to hit me at any point with my bus full of children.

ROSE: But other drivers at a local gas station like the design.

GREG PETERSON: It's fantastic. Less aggravation, less accidents - love it, the best money that you ever spent doing that for.

CYNTHIA DODSON: This type of intersection, it works really well because the traffic flows.

ROSE: That was Greg Peterson and Cynthia Dodson of Virginia. Reactions like that are gratifying for inventor Gilbert Chlewicki. You could say he's been working on this for most of his life.

CHLEWICKI: I mean, I was drawing roads when I was a little kid, and I would drive lanes wide enough for my Hot Wheels. And I would just use a map to kind of kind of guide me on what I wanted to draw. But something like this - the success of this is just unreal.

ROSE: Chlewicki first had the idea for the diverging diamond interchange when he was in grad school at the University of Maryland and presented the first major paper on it at a conference in 2003. I asked if he was disappointed that it's taken 20 years for the idea to go mainstream.

CHLEWICKI: I mean, honestly, for government and for complex things like the interchanges, this one's super-fast.

ROSE: Chlewicki is now employed by the Virginia Department of Transportation, where he's working on some new mutations of the diverging diamond - as he puts it, still playing with model cars and paper. Joel Rose, NPR News, Haymarket, Va.

(SOUNDBITE OF KEVIN HAWKINS SONG, "RED CAR") Transcript provided by NPR, Copyright NPR.

NPR transcripts are created on a rush deadline by an NPR contractor. This text may not be in its final form and may be updated or revised in the future. Accuracy and availability may vary. The authoritative record of NPR’s programming is the audio record.

Joel Rose is a correspondent on NPR's National Desk. He covers immigration and breaking news.