LED traffic lights may not be as safe as expected

The UD pilot study, published recently in the Institute of Transportation Engineers’ ITE Journal, found that traffic accidents at eight intersections in Middletown increased 71 percent between 1999 and 2007 after traffic signals were converted from light bulbs to LEDs. The researchers used a formula to predict that approximately 75 crashes would occur at the eight intersections after the change. Instead, there were 129 accidents.

“With all the benefits we know of with LEDs, we expected the crashes to go down,” said Deogratias Eustace, a University of Dayton assistant civil engineering professor. “But what you think and what you see from the data are very different.”

The study team, which included UD assistant math professor Peter Hovey and Middletown traffic engineer Valerie Griffin, said more research and a national sampling is needed to see if LEDs actually are the cause for the increased accidents or if other factors such as changes in traffic volume or patterns played a role. In addition, earlier LED signals are not as bright as those developed in the last few years, Eustace noted.

The study also did not look at the impact of weather conditions, he said. Because LEDs generate so little heat, they can be obscured by packed snow and ice, a problem in northern states. In April of last year, a truck driver ran a red light covered in snow at an intersection in a Chicago suburb and killed a 34-year-old woman turning left and injured four of her passengers.

The city of Dayton has been a national leader in the switch to the new traffic signals, with 95 percent of its system now LEDs. Assistant Public Works Director Steve Finke said the city has gotten calls to remove packed snow from lights, but he knew of no accidents caused by LEDs. About 80 percent of Montgomery County’s signals are LEDs, officials said.

Traffic signal bulbs account for about 90 percent of the total energy use at typical intersections, according to the UD study. Converting bulbs to LEDs can cut energy consumption by about 80 percent. They also help preserve lens covers and intersection wiring, and they appear brighter than conventional signals, especially in direct sunlight.

“LED traffic signals have become the national standard,” the group wrote in the study. “They are less expensive to maintain and provide more reliability than traditional incandescent bulbs. However, with all these benefits, if they deteriorate the intersection safety, they will be undesirable.”

Mike Spack, president of Spack Consulting and Traffic Data Inc. and adjunct professor in the University of Minnesota’s civil engineering department, called the study alarming on his blog “Mike on Traffic.” He, too, said he hoped the Federal Highway Administration further studies LEDs.

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