Nonfatal bicycle accident risk after an evening of alcohol consumption

Abstract

Introduction: After an evening of alcohol consumption, blood alcohol concentration (BAC) may reach intoxication levels above legal limits for operating a car or bicycle. In the Netherlands, legal limits for participating in traffic are 0.05% for experienced drivers and 0.02% for novice drivers. The purpose of this study was to determine bicycle accident risk of Dutch students after an evening of alcohol consumption. Methods: A survey was conducted among 800 University and college students in Utrecht, The Netherlands. The survey included retrospective questions concerning alcohol consumption on a typical night out and the start and end time of consumption. For those who travel home by bicycle, BAC was computed and relative risk of having a bicycle accident. Finally, they reported the likelihood (0 - 100 %) that they would consume less alcohol when police controls for drunk bicycling were comparable to those for car drivers (with a similar chance of getting caught and a similar fine for driving when drunk). Results: 761 surveys (95.3 %) were eligible for statistical evaluation. 690 students reported going to the pub for a night out, on average 1.6 times per week. 445 students (64.5 %) reported traveling home by bicycle often or always. They reported drinking an average of 6.8 alcoholic drinks (Standardized drinks contain 12 gram alcohol) and their mean (SD) BAC when traveling home was 0.95 (0.9)%. The percentage of past year accidents or injury among those traveling home by bicycle often or always but consumed no alcohol (BAC=0%) was 2%. Alcohol consumption significantly increased the risk of bicycle accidents (Odds ratio: 6.8). Odds ratio of having a bicycle accident increased exponentially when having a higher BAC: 2.5 (BAC = 0-0.2%), 6.8 (BAC = 0.2-0.5%), 6.0 (BAC = 0.5-1.0%), 16.4 (BAC = 1.0-1.5%) and 11.1 (BAC > 1.5%). Logistic regression analysis revealed a significant (p<0.006) relationship between alcohol consumption and the risk of a bicycle accident. Students who travel home by bicycle report that there is a 41.9% chance that they will consume less alcohol on a night out when police controls for driving drunk are the same as for car drivers. This was not related to BAC levels. Conclusions: On average, students have blood alcohol concentrations that are five-fold higher than allowed to participate in traffic. Nevertheless, most of them travel home by bicycle after an evening of alcohol consumption. This is of great concern, since the risk of having a bicycle accident increases with higher BAC levels.