Summary of NHTSA Report on Alcohol and Motorcycle Riding
Results
The results showed that performance for several dependent measures of riding
performance were impaired at the BAC .08 condition.
• In the offset weave (slalom) task, participants missed or hit more pylons
and had smaller passing distances around the pylons in the BAC .08
condition compared to the other alcohol and placebo conditions.
• In the hazard avoidance task where a warning was provided when the
motorcycle was 1.5 seconds away from the hazard, participants had
slower reaction times in both the BAC .08 and .05 conditions compared to
the placebo condition.
• In the hazard avoidance task where a warning was provided when the
motorcycle was 2.5 seconds away from the hazard, participants in the
BAC .08 and .05 conditions passed at a closer distance to the obstacle than
in the placebo or BAC .02 conditions. For both hazard tasks, riders turned
in the wrong direction more often in the BAC .08 condition.
• In the curve circuit task, there was a significant main effect of BAC for
maximum speed and speed variability. Although post-hoc tests were not
v significant, participants in all alcohol conditions tended to have faster
maximum speeds and increased variability in speed in the circuit
compared to the placebo condition. Participants in the BAC .08 condition
were also more likely to cross outside the curve circuit boundaries than
participants in other conditions.
• In the emergency stop task, participants in the BAC .05 condition reached
maximum deceleration faster than participants the other alcohol
conditions. This difference was significant between the BAC .05 and .08
conditions. Finally, there was a significant change in motorcycle position
during the emergency stopping task between the BAC .08 and .02
conditions, where the BAC .08 condition showed more deviation in their
stopping path compared to the BAC .02 condition.
• Participants reported requiring more effort to ride and complete the tasks
in the BAC .08 condition when compared to the placebo condition. Their
levels of subjective intoxication also increased significantly with
increasing BACs. Participants reported that their perceived levels of
performance impairment was higher for the BAC .05 and .08 conditions
compared to the placebo and BAC .02 conditions. Participants in the BAC
.05 and .08 conditions also reported they would be less willing to ride a
motorcycle for any reason.
Conclusions
This study demonstrates some changes in riding behavior in response to alcohol
consumption that may be construed as impairment relative to standard
performance and the self-assessment of riders. Most of the impairing effects on
riding performance were evident at the per se alcohol limit of BAC .08. However,
some of these same impairing effects were also evident in the lower BAC .05
condition. Admittedly, the effect sizes (Eta2) calculated for the significant main
effect of alcohol may be considered small (a range of 2% to 8% of variance was
accounted for by the alcohol effect). Given that this study used experienced
riders performing highly practiced tasks on a closed course at low to moderate
BACs, the effect of alcohol on motorcycle control and rider behavior was modest
except when task demand was high (offset weave), time pressure was high
(hazard avoidance for near obstacles), and tolerances were constrained (circuit
track). Larger impairments may be expected with less experienced riders, on
less familiar roads, with more complex and novel tasks at higher alcohol doses.
Although the participants’ self-reports suggest that riders may be aware of the
intoxicating and impairing effects of alcohol, this study cannot conclude that
corollary self-regulation would be sufficient to mitigate crash risk. Similarly,
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more research is needed to determine real-world implications of BAC during the riding experience.