Superstreets make traffic 20% faster by eliminating left turns

The 'Superstreet' intersection design has been lurking around transportation planning textbooks for decades, but North Carolina State University has been testing it out recently and as long as you never want to turn left, it promises to make intersections much more efficient.

Superstreet intersections are designed for situations where you've got a major road intersected by a bunch of smaller roads. What generally happens in these situations is that the people on the smaller roads trying to get across the major road have to wait forever, or if there's a traffic light, all of the traffic on the main road has to stop and wait for just a couple cars to get across. This is horribly inefficient, not to mention frustrating.

The Superstreet intersection attempts to solve this problem by entirely doing away with left turns and preventing streams of traffic from directly crossing each other. To cross a Superstreet, traffic from side roads must first turn right, joining the main flow of cars. A dedicated u-turn lane allows you reverse your direction, at which point you can continue straight (effectively making a roundabout left turn), or turn right, which gets you across the intersection.



At first glance, this probably seems pretty inconvenient. But the idea is that even if you want to turn left, you're actually saving a bunch of time by not having to sit and wait for a light. Superstreet intersections can operate without any traffic lights whatsoever, but signals that can stop individual streams of traffic (as opposed to the entire intersection) can make sure that things don't get backed up.

Comparative studies of Superstreet intersections and regular intersections by North Carolina State University have shown that overall, cars move through Superstreet intersections about 20% faster. There are 43% fewer accidents, and 63% fewer accidents that resulted in injuries. I'm sure it's going to be difficult, if not impossible, to convince drivers that making three extra turns just to go in a straight line is actually the most efficient way to go, but for roads that are already bulging with cars, it might be worth the effort.