The purpose of this report is to analyze the crash-reduction benefits of LED stop lamps and LED center high-mounted stop lamps (CHMSL) using real-world crash data. Previous work on this subject included laboratory experiments that suggest LED lamps were more beneficial than incandescent lamps at preventing rear-impact collisions. NHTSA statistically compared the overall ratio of rear-impact crashes to a control group of frontal impacts before and after the switch to LED. Overall, the analysis does not support a firm conclusion about whether LED stop lamps and LED CHMSL are more effective than incandescent lamps. The main analysis shows a significant overall 3.6% reduction in rear-impact crashes with LED. On the other hand, a non-parametric analysis not only fails to show improvement in significantly more than half the models, but actually shows an increase in rear impacts with LED for 9 of the 17 make-models that switched to LED. It was just the favorable results for high-sales vehicles such as Honda Accord that pulled the overall result into the plus. Furthermore, and perhaps most important, none of these 17 make-models is a “clean” switch pair that shifted to LED without changing anything else. All of the switch pairs shifted to LED at the same time that they changed the rear-lighting configuration and/or redesigned the vehicle. Basically, the crash data probably won’t support a firm conclusion until we have more switch pairs, including some “clean” switch pairs. (Author/publisher)
Abstract