This purpose of this report is to determine the effect of rear turn signal color on the likelihood of being involved in a rear-end crash. Federal Motor Vehicle Safety Standard No. 108 allows rear turn signals to be either red or amber in color. Previous work on this subject includes laboratory experiments and analyses of crash data that suggest amber rear turn signals are beneficial. The present study was designed around the concept of “switch pairs” – make-models of passenger vehicles were identified that had switched rear turn signal color, and crash involvement rates were computed before and after the switch. This method should control for extraneous factors related to vehicle and driver characteristics. Crash data from NHTSA's State Data System was used in the analysis. The principal finding of the report is that amber signals show a 5.3% effectiveness in reducing involvement in two-vehicle crashes where a lead vehicle is rear-struck in the act of turning left, turning right, merging into traffic, changing lanes, or entering/leaving a parking space. The advantage of amber rear turn signals is shown to be statistically significant. (Author/publisher)
Abstract