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The influence of rear turn signal characteristics on crash risk

DOT HS 811 037

In: Performed by University of Michigan Transportation Research Institute, sponsored by National Highway Traffic Safety Administration

Authors: John M. Sullivan, Michael J. Flannagan.

The relationship between the relative risk of a rear-end collision involving a turn, merge, or lane change maneuver and the characteristics of the rear turn-signal configuration was examined using rear-end collision crash data pooled from seven States. To perform the analysis, a detailed database of rear signal characteristics was developed for the vehicles most frequently involved in crashes among five of the States. The signal lamp characteristics were combined with other factors contained in the crash record in a stepwise logistic regression that modeled the odds of a rear-end collision while performing a turn- signal-related maneuver as a function of all of these factors. Two contrast groups were used as the denominator of the odds ratio in separate analyses. The first contrast group was comprised of the striking vehicles involved in turn-signal-related rear-end collisions. The second contrast group was comprised of rear-struck vehicles not engaged in turn-signal relevant maneuvers. The first analysis suggests that there is an association between amber turn signals and a reduction of between 3 and 28 percent in the odds of being the struck (versus striking) vehicle in a turn-signal- relevant maneuver. The second analysis found no association between turn signal color and the odds of being struck in a turn-signal-relevant maneuver. The differences in the two analyses are discussed in terms of how well the respective contrast groups are insulated from potential effects of turn signal configurations. Additional analyses substituted vehicle series name with body style as a predictor in the model, and examined turn signal characteristics in vehicles that have been produced with both amber and red turn signals at different times. Although the analysis suggests that there may be a safety benefit associated with amber turn signals, it is unclear that turn signal color itself is completely responsible...

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