Understanding the role of alcohol and drugs on bicyclist injury severity

This study examined the impact of alcohol and drug use on bicyclist injuries caused by bicycle-motor vehicle crashes. We used six-year data from the city of Jacksonville, Florida. Descriptive statistics results showed that with data involving alcohol/drugs there was 38.93 percent incapacitating injury or fatal outcomes while with the data not involving alcohol/drugs there was only 12.36 percent incapacitating injury or fatal outcomes. Due to this discrepancy, crashes involving alcohol and/or drug use and those not involving alcohol and/or drug use were analyzed separately to identify whether there exist specific factors explaining the discrepancy in injury severity among the two groups. In addition to estimating separate multinomial logit (MNL) models for each data set, a model was estimated using combined data. Both MNL models estimated with separate data indicated that the following factors which were identified as significant with combined data were not significant: bicycle on roadway and at-fault motor vehicle changing lanes. However, whether the crash occurred at the intersection was among the significant variables in the models estimated with separate sub-data but not in the combined-data analysis. To compare the effect of the variables on injury severity for crashes involving alcohol/drugs and those not involving alcohol/drugs, we computed elasticities. The results indicated that variables that are significantly affecting the injury outcome when considering crashes involving alcohol and/or drug use are not necessarily significant when considering crashes not involving alcohol and/or drug use. Even when a variable was found to be influential on both data sets, there was a difference in what bicyclist injury severity is impacted and how it is impacted. The only factors found to have effect on severity for both data sub-sets (although inconsistent on the direction of the effect on some injury levels) was whether or not a crash occurred at an intersection.