Crash Reduction Effects of Flashing LED Stop Signs

A flashing LED stop sign is a regular octagonal stop sign with flashing light-emitting diodes (LED) on its vertices. The hope is that by increasing the conspicuity of the stop sign the frequency of violations, and related intersection crashes, will be reduced. At present however there does not appear to be conclusive evidence regarding the crash reduction effects of this treatment. In this paper, the authors implemented a hierarchical Bayesian approach to correct the regression-to-the-mean bias and estimate the right-angle crash reduction factor for those intersections installed flashing LED stop signs in Minnesota. The treatment and reference group data were prepared based on Minnesota District Engineer and County Engineer survey, Highway Safety Information System data, Minnesota Crash Mapping Analysis Tool data, and Google Maps observations. Three models with different predictors were fitted and five covariates were found to be significant, including the major road ADT, the minor road ADT, the major road speed limit, the minor road speed limit, and the number of legs in the intersection. The point estimate of crash reduction factor indicates more than 40% reduction. It has a wide confidence interval due to the sample size of after treatment data and the probability that it is greater than 0 is approximately 95%, suggesting that a decrease in the frequency of right-angle crashes is associated with installation of flashing LED stop signs, but that the magnitude of this reduction remains uncertain. Once more after-treatment data are available in the future, the precision of crash reduction factor estimate could be improved.