Motorcycles and alcohol

Deputy Secretary of Transportation Thomas Barrett (seated) discusses motorcycle safety with U researchers Craig Shankwitz and Janet Creaser.

Photo courtesy of the Center for Transportation Studies

From eNews, September 25, 2008

This summer and fall, when gas prices hit an all-time high and warm weather beckoned riders to the road, motorcycles and scooters were more popular than ever. But statistics from the National Highway Traffic Safety Administration (NHTSA) show that while motorcycles account for only 3 percent of motor vehicle registrations, they make up 11 percent of total motor vehicle fatalities.

Researchers from the HumanFIRST and Intelligent Vehicles Laboratory recently collaborated to study the effects of alcohol on motorcyclists. The NHTSA and University of Minnesota's Intelligent Transportation Systems Institute funded the study.

While a large body of research has been devoted to detailed analysis of how alcohol interferes with automobile operation, relatively little work has been completed on the question of how alcohol affects the skills required to operate a motorcycle.

One reason for the discrepancy is the difficulty in accurately evaluating motorcycle operation skills without endangering the safety of the rider. Realistic driving simulators based on motorcycles rather than four-wheeled vehicles are virtually unknown, and in-vehicle testing is restricted by the obvious hazards facing an impaired rider, as well as strict laws prohibiting vehicle operation while intoxicated.

To overcome these restrictions, the Minnesota team retrofitted a motorcycle with a safety mechanism and a remote data-acquisition system and conducted the study at the Minnesota Highway Safety and Research Center in St. Cloud--the only place in Minnesota where an alcohol-impaired research participant can legally operate a motorcycle.

The motorcycle, a 2000 Honda Shadow VT1100a, was first equipped with a system of mechanical outriggers capable of preventing it from falling sideways in the event that a rider lost his balance. Then a Motorcycle Data Acquisition system was rigged to it to monitor the handling of the bike's controls (throttle, brakes, and steering) and the accelerometers that measure forward and lateral movements. The researchers also used a motorcycle helmet that was equipped with a miniature video camera and sensors.

The research team recruited 24 male study participants who had a minimum of five years of motorcycling experience and drank alcohol at least once a week but had no history of alcohol dependence. After training to familiarize them with the research motorcycle, the riders participated in three half-day test sessions during which they drank alcohol to reach a blood-alcohol concentration of .02, .05, or .08 g/dL (the latter is the legal limit in all 50 states), or were given a placebo (alcohol applied to the rim of a glass containing a non-alcoholic beverage).

After consuming the alcoholic beverage or the placebo, the participants rode through a test course developed in collaboration with motorcycle instructors from the Minnesota Motorcycle Safety Center. The course included both routine riding situations and the need for emergency maneuvers. Data from both baseline (non-alcohol) rides and rides after consuming alcohol were gathered for each participant.

The researchers found that the impairing effects on riding performance were most evident at the .08 blood-alcohol level. However, many of these same impairing effects were also evident in participants with a .05 blood-alcohol level.

And although self-reports by the participants indicated that many riders may realize when alcohol is affecting their riding performance, the researchers caution that the evidence does not mean that self-regulation is sufficient to mitigate the increased crash risk due to riding after drinking.

"It is likely that in the real world--with concurrent distractions and without the motivation to perform for an experiment--that impairment effects would be larger," the researchers noted. "Thus, more research is needed to determine real-world implications of [blood-alcohol level] during the riding experience."

A final report on the project is being prepared for publication.

Edited from CTS Research E-News, September 2008, a publication by the Center for Transportation Studies