The University of Dayton 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 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 UD assistant civil engineering professor. “But what you think and what you see from the data are very different.”
The study team, which included Middletown traffic engineer Valerie Griffin, said more research and a national sampling are needed to see if LEDs actually are the cause for the increased accidents or if other factors, such as the 161 percent increase in traffic volume at one intersection, 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. Because LEDs generate so little heat, they can be obscured by packed snow and ice, a problem in northern states.
Middletown has spent seven years and $16,800 to convert 112 traffic signals to LEDs, an effort officials say is saving up to 90 percent on electric bills. Griffin said the original purpose of the study was to show if the new lights were safer by reducing maintenance and thereby reducing work zones and worker exposure to traffic. However, such a small sample size couldn’t conclusively show the benefits.
“Just because LEDs haven’t shown an increase in safety doesn’t mean they have been detrimental to safety. I believe they will help over time, but you have to make it a more regional or national study,” she said.
Griffin also noted incandescent bulbs do not meet current industry standards and are no longer manufactured, which requires cities to install LEDs or other equivalent when replacing lights.
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 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.”
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