Safety Evaluation of Converting Traffic Signals from Incandescent to LED Bulbs

摘要

Data from 282 signalized intersections in Charlotte were used to examine the safety effect of convertingthe signals to composite light emitting diode (LED) bulbs. An empirical Bayes before-after method wasused for the evaluation. Since this was a “blanket” installation by the city of Charlotte, a comparisongroup of stop controlled intersections were used to account for possible trends during the study period.Crash modification factors were estimated for 3 and 4 leg intersections for 8 different crash typesincluding crashes during dawn, dusk, and dark conditions. For 3 leg intersections, all the CMFs werehigher than 1.0 indicating a possible increase in crashes due to LEDs. However, none of these CMFswere statistically different from 1.0 at the 0.05 significance level. For 4 leg intersections, the CMFsassociated with rear-end crashes were lower than 1.0 and statistically significant at the 0.05 level,indicating a reduction in these crash types due to the LEDs. There was substantial difference among thesites in terms of the effect of the LEDs. The reasons for these differences are not known at this time.Future research could investigate whether LEDs are more or less beneficial depending on thecharacteristics of the intersection including type of area, sight distance, traffic volume, and phasingscheme.