Science-- there's something for everyone

Saturday, January 22, 2011

Streets without left turns

City planners who wish to increase traffic efficiency and safety would do well to consider designing ‘superstreets’ according to a study by researchers at North Carolina State University.

Superstreets are roads that are designed to eliminate left turns. Rather than making a left at an intersection, drivers must first turn right and then make a u-turn. Although this sounds counterintuitive it actually saves time. In fact, travel time on superstreets is 20% less than on conventional streets. Even more important, superstreet intersections lead to 50% fewer collisions.

The idea of eliminating left turns is not new. Roundabouts, junctions that allow drivers to circle around to the left or right without making an abrupt turn, have been shown to be safer and more efficient than right-angle intersections. They are currently more common in Europe and Asia, but are becoming more popular in North America.

Even on traditional streets, some companies have initiated ‘no left turn’ policies for their drivers. Again, it seems like eliminating left turns would require time-consuming circuitous routes. Not so. UPS, for example, claims to save three million gallons of gas each year by eliminating lefts. UPS drivers do rely on route-planning software to get them to their destinations efficiently. You can’t get that kind of time and energy savings by blindly turning right instead of left at each intersection.

Here's an example of a superstreet interesection:


  1. But U-turns require a turn to the left, if these new streets are to be as energy efficient as they claim, would they not also make the U-turners spin around to the right?

  2. According to the diagrams, there are special u-turn lanes that don't cross over the other traffic.