Role of alcohol and marijuana use in the initiation of fatal two-vehicle crashes

Abstract Purpose To assess individual and joint effects of alcohol and marijuana on the initiation of fatal two-vehicle crashes. Methods Data on 14,742 culpable drivers (initiators) and 14,742 nonculpable drivers (noninitiators) involved in the same fatal two-vehicle crashes between 1993 and 2014 were obtained from the Fatality Analysis Reporting System. Multivariable conditional logistic regression models were used to assess the association of driver use of alcohol, marijuana, or both with fatal crash initiation with adjustment for demographic variables. Results Initiators were significantly more likely than non-initiators to test positive for alcohol (28.3% vs. 9.6%, P P P Conclusions Alcohol and marijuana each play a significant role in fatal crash initiation. When used in combination, alcohol and marijuana appear to have a positive interaction effect on the risk of fatal crash initiation on the additive scale.