Researcher suggests banning cross-traffic turns

An American researcher is suggesting that cities could make traffic flow better and have fewer emissions if they reduced or eliminated turns across the flow of traffic, so in our case turning right.

Vikash V Gayah, Associate Professor of Civil Engineering at Penn State University, points to logistics firm UPS which changed its routes in 2004 to minimise left hand turns (across the traffic when you drive on the right), which it says led to it saving ten million gallons of fuel, and 20,000 tonnes of carbon emissions. It says because drivers don’t waste time waiting to cut across traffic allows them to deliver 350,000 additional packages.

“As a transportation engineering professor at Penn State, I have studied traffic flow on urban streets and transportation safety for nearly a decade,” Prof Gayah writes in The Conversation. “Part of my work focuses on how city streets should be organised and managed. It turns out, restricting left turns at intersections with traffic signals lets traffic move more efficiently and is safer for the public. In a recent paper, my research team and I developed a way to determine which intersections should restrict left turns to improve traffic.”

He writes that intersections are dangerous because they are where cars, often moving very fast and in different directions, must cross paths, and approximately 40% of all crashes occur at intersections, including 50% of crashes involving serious injuries and 20% of those involving fatalities. “Traffic signals make things safer by giving vehicles instructions on when they can move,” he writes, but “If left turns did not exist, the instructions could be very simple: For example, a north-south direction could move while the east-west direction was stopped and vice versa. When drivers make left turns, they must cross oncoming traffic, which makes intersections much more complicated.”

He explains that having to drive further because you can’t cut across traffic would be off-set by a smoother traffic flow, and that algorithms exist to work out the best ones to choose to have maximum effect on traffic.

“So the next time you are sitting stuck in traffic behind someone waiting to make a left turn, know that your frustration is justified,” he concludes. “There is a better way. In this case, the answer is simple – get rid of the left turn.”

(Picture – Transport Technology Forum)


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