More than 60% of traffic collisions at intersections involve left turns. Some U.S. cities – including San Francisco, Salt Lake City and Birmingham, Alabama – are restricting left turns.

Dr. Vikash Gayah, a professor of civil engineering at Penn State University and the interim director of the Larson Transportation Institute, discusses how left turns at intersections cause accidents, make traffic worse and use more gas.

The Conversation has collaborated with SciLine to bring you highlights from the discussion, edited for brevity and clarity.

How dangerous are left turns at intersections?

Vikash Gayah: When you make a left turn, you have to cross oncoming traffic. When you have a green light, you need to wait for a gap in the oncoming traffic before turning left. If you misjudge when you decide to turn, you could hit the oncoming traffic, or be hit by it. That’s an angle crash, one of the most dangerous types of crashes.

Also, the driver of the left-turning vehicle is typically looking at oncoming traffic. But pedestrians may be crossing the street they’re turning on to. Often the driver doesn’t see the pedestrians, and that too can cause a serious accident.

On the other hand, right turns require merging into traffic, but they’re not conflicting directly with traffic. So right turns are much, much safer than left........

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