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Effects of turn-signal color on reaction times to brake signals


Authors: Juha Luoma, Michael J. Flannagan, Michael Sivak, Masami Aoki, Eric C. Traube

This experiment was designed to compare reaction times to brake signals when they appear with red or yellow turn signals. The laboratory study simulated a daytime driving condition. The subject's task was to respond as quickly as possible to the onset of peripherally presented brake lamps (but not to turn signals), while engaged in a central tracking task. There were three lamp conditions: brake lamps alone, brake lamps while turn signal was on, and a turn-signal lamp alone. Thus, the subject's task required an immediate response in the first condition, a delayed response in the second (only after the brake lamps came on, not to the turn signal), and no response in the third condition. Turn signals were presented at two levels of luminous intensity. The results showed that reaction times to brake signals were significantly shorter when the brake signals were presented in the context of yellow turn signals than when they were presented in the context of red turn signals. Averaged over both levels of luminous intensity and conditions with and without turn signals, the difference between yellow and red was 110 ms. The colors of turn signals had an effect whether or not the turn signal was on, but the effect was greater when it was. Older subjects were affected more by the color of turn signals than were younger subjects. In conclusion, yellow turn signals are beneficial in situations simulated in this experiment. However, the present findings are directly applicable only to a situation where all vehicles have yellow turn signals and tail lamps are not energized.