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Effects of Alcohol on Motorcycle Riding Skills

Presentation by Janet Creaser, Research Fellow, HumanFIRST Program, University of Minnesota

September 24, 2009

Alcohol intoxication is a significant risk factor in fatal crashes for passenger cars and motorcycles. Field research has shown that run-off-road crashes and loss-of-control crashes for motorcycles increase at a blood alcohol level of 0.05 percent—which is below the U.S. legal drinking limit of 0.08 percent. At present, however, there is limited objective data on which motorcycle riding skills are impaired by alcohol.

At the September 24 Advanced Transportation Technologies seminar, HumanFIRST Program research fellow Janet Creaser presented findings of a 2006 study she and a U of M research team conducted for the National Highway Traffic Safety Administration. The study measured the effect of alcohol impairment at four blood alcohol content (BAC) levels at and below BAC 0.08 on the basic riding skills of motorcyclists on a controlled course. Questionnaires were used to assess riders’ awareness of their level of alcohol impairment and how that affected their decision-making.

Using a test motorcycle modified by the Intelligent Vehicles Laboratory, researchers ran motorcyclists with blood alcohol levels of 0.02, 0.05, and 0.08 through a test track based on training tasks from the Motorcycle Safety Foundation training courses. Riders were measured on their responses to four tests: control and maneuverability, hazard avoidance, curve negotiation, and emergency stops.

Riders showed the greatest impairment on tasks with complex information, high time pressure, or tight space constraints, Creaser said. For example, in the hazard-avoidance test, drivers had to dodge an obstacle with a 1.5-second warning, a high time pressure. Impairment was seen at the BAC 0.08 and 0.05 levels for several measures, including response time to the hazard-avoidance task, speed maintenance during the curve circuit, and ability to stop in a straight line during the emergency stop.

Because the test track was designed with typical types of motorcycle crashes in mind such as running off the road, going off curves, and loss of control, Creaser said the results showing impairment in the test tasks are indicative of the types of crashes seen among motorcycle riders in the real world. The observed impairment in the test track study, where tasks were low-speed (less than 25 mph) and the environment highly controlled, would be magnified in the real world where motorcyclists are often driving at much higher speeds, she noted.

“If you have a detriment in response time due to alcohol, you travel a lot further at 50 mph than you do at 10 mph, which could be the difference between hitting an obstacle or getting out of the way,” she said.

A follow-up questionnaire had drivers assess how impaired they were and their willingness to drive in an impaired condition. The surveys found that drivers with BAC levels of 0.05 and 0.08 knew they were impaired and would be less likely to get on a bike. But focus group data from other studies has shown that in a real-world situation, external factors would likely influence their decisions to ride, Creaser said.

The study concluded that riders show impairment due to alcohol on certain skills at BAC levels of 0.05 and 0.08, and those results, combined with recent crash data, suggest that motorcyclists are potentially at an increased risk of a crash even below legal BAC levels.