Motorcycle Riding Impairment at Different BAC Levels

Principal Investigator(s):

Nic Ward, Former U of M Researcher, Mechanical Engineering


Project summary:

Alcohol is known to disrupt the effect of neurotransmitters and impair various psychomotor skills; therefore alcohol intoxication is a significant risk factor for fatal crashes, especially when riding a motorcycle. At present, there is sparse research on the impairing effects of alcohol on skills involved in motorcycle control. This study was designed to measure to effect of alcohol (up to BAC 0.08%) on a broad set of basic riding skills. These riding skills were assessed on a test track with task scenarios based on the Motorcycle Safety Foundation's (MSF) training program. The study used a balanced incomplete block design to remove confounding artifacts (learning effects) by randomizing four BAC levels across three test days. Performance was characterized in terms of riding strategy used to cope with the effects of alcohol as a neurological stressor and the amount of resulting impairment with reference to specified performance standards. The analysis controlled for rider gender and age, riding skill, and drinking history. The results showed there were observable changes in motorcycle control and rider behavior in response to alcohol that are indicative of impairment. In general, intoxicated riders demonstrated longer response times and adopted larger tolerances leading to more task performance errors. Riders appeared to protect bike stability at the expense of other task performance and riders tried harder (where possible) to fully or partially compensate for the negative effects of alcohol. Most of the alcohol effects were evident at the per se BAC .08 g/dL level, but some effects were observed at the lower BAC .05. Given that this study used experienced riders performing highly practiced tasks with low to moderate levels of alcohol, the effect of alcohol on motorcycle control and rider behavior were modest except when task demand was high (offset weave), time pressure was high (hazard avoidance for near obstacles), and tolerances were constrained (circuit track). The practical significance of the findings is discussed in terms of study constraints.

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