Time-of-day variations and the temporal instability of multi-vehicle crash injury severities under the influence of alcohol or drugs after the Great Recession

Using data of multi-vehicle crashes with drivers under the influence of alcohol/drugs in North Carolina from 2008 to 2017, this paper explores time-of-day variations (daytime vs. nighttime) and temporal instabilities of factors affecting alcohol/drug-impaired crash injury severities during three crash cycle phases after the Great Recession. Random parameters logit models with heterogeneity in the means and variances are utilized to identify significant factors, explore unobserved heterogeneity, reveal correlations between factors, and suggest possible impacts of economic conditions on the factors. Different likelihood ratio tests indicate that the effects of factors vary significantly across time-of-day and economic-related cycle periods. Significant time-of-day variations imply more severe injury alcohol/drug involved crashes during the nighttime compared to the daytime. Meanwhile, temporal instabilities are also observed in marginal effects of several factors across three-cycle periods. Proficient and cautious elder drivers were safer than young drivers during the depression period. Also, both depressing and expanding periods could affect the involvement of alcohol/drugs for drivers. Shifts in alcohol/drug use behaviors underscore the importance of accounting time-of-day variations, temporal instabilities, and heterogeneity in the means and variances inherent in alcohol/drug-impaired crash factors after the Great Recession. The insights of this study should be valuable to improve specific enforcements, qualify punishments, organize targeted campaigns, and design other preventive activities for alcohol/drug-impaired crashes.