No driver loves a left turn against traffic. They’re just a pain, especially if you’re trying to get on a highway and have no other options but to wait around hoping for a break in the stream of cars. But the left turn to a highway on-ramp may soon be a thing of the past, according to CityLab. More and more areas are embracing divergent diamond interchanges, an odd-looking road configuration that makes funneling traffic onto expressways far safer.
The diverging diamond interchange involves criss-crossing lanes that mean no more turns against traffic. Instead, traffic flows around medians and merges together in ribbons that allow you to navigate in any direction, peeling off to merge onto the on-ramp rather than making left-hand turns at a right angle. As a result, traffic doesn’t have to stop as often—sort of like with a roundabout design. Pedestrians and bikes flow the same way, separated from traffic, meaning they, too, have to stop less often. Like so:
The idea was first proposed in the early 2000s by a transportation graduate student, but it's only now beginning to catch on in North America. There are almost 90 locations throughout the U.S. where they’re either in use or in the works. The city of Calgary just opened one, as did Sarasota, Florida, and Washington County, Pennsylvania.
Though it takes some getting used to, the design has real safety impacts. In the first five years of the first one of these interchanges in the U.S.—in Springfield, Missouri—left turn-related crashes were totally eliminated, and total car crashes were reduced by 46 percent. The Department of Transportation also found that these road designs significantly reduce the cost of interchanges, since they require fewer lanes to handle heavy flows of traffic.
Cheap and safe? Sounds like you’ll be seeing a lot more diverging diamonds on your road trips.