Changes to South Dakota Traffic Signals May Increase Crashes

Traffic-signal upgrades intended to smooth traffic and improve safety in Sioux Falls, S.D., appear to have slightly increased the number of vehicle accidents.

The city has installed flashing yellow left turn arrows at 30 intersections since 2010. The blinking signal permits drivers to turn left after yielding to oncoming traffic and pedestrians, the Argus Leader reported.

U.S. Highway Administration studies have shown that drivers are more cautious when facing a flashing yellow arrow compared to a solid green light. But an analysis of crash data by the newspaper found that nearly 20 intersections where the flashing signals were added show a 7 percent overall increase in accident rates.

City traffic engineers are hoping the numbers just reflect a learning curve. But some residents think the blinking signals are confusing drivers.

“They think they have to rush through,” said Ray Wiener, who’s witnessed confusion among drivers from his home near an intersection.

Heath Hoftiezer, principal engineer at City Hall, said there several potential reasons for increased crash rates. He said the data could reflect increased traffic, faster speeds or maybe just more time needed for drivers to get used to the signal change.

“There’s a learning curve every time we switch one of these out,” Hoftiezer said.

He said that most intersections with designated turn lanes will eventually have the flashing yellow arrow, but with the cost of up to $10,000 a light, drivers have time to get used to existing ones.