The April 2010 edition of the ITE Journal has an interesting article in it about LED traffic signal indications (titled Analyzing the Effects of LED Traffic Signals on Urban Intersection Safety). The authors (Eustace, Griffin, & Hovey) found a 71% increase in crashes due to replacing incandescent light bulbs with LED indications. I normally skim the ITE (Institute of Transportation Engineers) Journal, but this article caught my eye and I read the whole thing.
The authors studied the crashes at ten intersections in Middletown, Ohio where the incandescent bulbs were replaced with LED indications in 2003 and 2005. There are two pages of statistical analysis related to the empirical Bayes method (assuming a negative binomial distribution) used. This is a little over my head, so I'll trust the analysis is correct.
There is a relatively small sample size and there could be other factors contributing to the increased crash levels, but this is still an alarming study. I hope FHWA and other agencies will study this further. Traffic engineers assumed the brighter LED indications would be safer than incandescent bulbs(because of better visibility – the issue of snow sticking to them aside). We need to go back to the drawing board if the current style of LED indications are causing a 71% increase in crashes.