Safety rules allow automakers to use either red or amber rear turn signals on their vehicles, and a new federal study indicates that amber is the better choice to reduce rear-end crashes. Researchers estimate that amber-tinted signals reduce such crashes by 5.3 percent compared with red.
The National Highway Traffic Safety Administration identified 26 vehicle models with turn signal color changes during model years 1981-2005. Researchers compared crash rates before and after the change. The crashes involved 2 passenger vehicles where the lead one was turning, changing lanes, merging into or exiting from traffic, or entering or leaving a parking lot. Specifically, the researchers compared the odds of being struck among vehicles with amber versus red signals. A separate odds ratio was calculated for each model and then averaged to estimate overall effects.
The effectiveness of amber turn signals for individual models ranged from a 33 percent reduction in rear crash involvement to a 36 percent increase (approximately three-quarters were estimated reductions). Overall effectiveness was calculated at a 4.9 percent crash risk reduction. To control for possible effects of vehicle design changes, researchers repeated the analysis, restricting it to models with just a change in turn signal color without other design changes. The result was a statistically significant 5.3 percent reduction in crash risk. This is in line with previous research showing amber rear turn signals to be more effective in reducing the likelihood of rear crashes. European automakers have been required to use this color since 1967.
The topic of amber rear turn signals is included in the agency's July 2009 priority plan, which closed for comment Aug. 31. Regulators expect to consider the next steps by the end of the year.