When traffic is clogged at a downtown intersection, there may be a way to reduce some of the congestion: Eliminate a few left turns.

According to Vikash Gayah, associate professor of civil engineering at Penn State, well-placed left-turn restrictions in certain busy intersections could loosen many of the bottlenecks that hamper traffic efficiency. He recently created a new method that could help cities identify where to restrict these turns to improve overall traffic flow.

«We have all experienced that feeling of getting stuck waiting to make a left turn,» Gayah said. «And if you allow these turns to have their own green arrow, you have to stop all other vehicles, making the intersection less productive. Left turns are also where you find the most severe crashes, especially with pedestrians. Our idea is to get rid of these turns when we can to create safer and more efficient intersections.»

By selectively restricting left turns, but not banning them entirely, drivers may simply need to find alternate routes to their destinations in certain areas, Gayah said. Some may be required to travel a few extra blocks, but Gayah believes more efficient traffic flow through busy intersections offsets the additional distance.

For urban planners, he added, determining where to place the restrictions is a balancing act between intersection productivity and increased travel lengths. With so many restriction possibilities to consider, finding the most efficient layout may prove difficult.

«For example, if you just have 16 intersections to consider, each with a choice to allow or not allow left turns, that is already 65,000 different configurations,» Gayah said. «It gets even more complicated when you consider that traffic flows from one intersection to the next, so decisions depend on one another. There ends up being so many possible answers that we can never find the best one.»

Gayah’s new method relies on heuristic algorithms, which use shortcuts to find solutions that nearly approach, but are not guaranteed to be, an optimal outcome.

Story Source: Materials provided by Penn State. Original written by Tim Schley. Note: Content may be edited for style and length.