The Effect of Blood Alcohol Concentration on Motorcycle Crash Characteristics

This paper examines differences in accident characteristics and causation at different blood alcohol levels among 372 accident involved motorcycle riders who were tested shortly after they crashed. The subjects were part of a large, prospective, in-depth study of 1082 accident-involved motorcyclists in Thailand in which investigators went to the scene immediately after a crash to collect and analyze evidence in order to determine how the crash occurred. The crash characteristics considered here include those that have been identified as typical of alcohol-involved motorcycle crashes including collision type, loss of control, running off the road, traffic control violations, precrash & crash speeds. The causation factors include primary cause factors and rider attention failures. Approximately 60% of 372 riders tested positive for alcohol. The frequency of inattention just before the crash increased steadily and almost linearly with increasing BAC. However, most other crash characteristics showed a sudden change in the frequency of occurrence near the 50 mg/dL (.05%) level, then remained relatively steady at higher BAC levels. Compared to non-drinking riders, those with BAC > 50 mg/dL were more likely to be in single vehicle crashes, more likely to lose control, to run off the road, to be inattentive before crashing and to be the primary or sole cause of their accident. These findings demonstrate that when rider blood alcohol level approaches 50 mg/dL (.05%), the rider becomes a significantly greater threat to himself.