The effect of license plate number-based vehicle restrictions on crash frequency

This study investigates the effects of license plate-based vehicular circulation restrictions, known as "peak-and-plate" policies, on urban traffic crashes in Medellín, Colombia. Although such policies are widely implemented to reduce congestion and emissions, limited research has examined their unintended safety impacts on crash frequency before and during the restriction periods. Considering high-resolution crash data from 2008 to 2022, this study evaluates the temporal effects of these restrictions on crash frequency across different hours, months, and weekdays. Statistical preprocessing and hierarchical clustering techniques were applied to discover crash temporal patterns, and negative binomial, pooled, fixed effects, and random effects models were tested to account for overdispersion and panel structure in the data. Results reveal that crash frequencies increased consistently in the 30 min preceding the enforcement of circulation restrictions, particularly during the morning hours. Surprisingly, crash rates remained elevated during the restriction period, contrary to expectations that reduced vehicle volume would lower crash occurrences. These findings suggest the presence of confounding behavioral, spatial, or enforcement-related factors. Additionally, monthly and weekly crash patterns correlate with seasonal variations, holidays, and changes in traffic volume, emphasizing the importance of context-aware traffic policies. Statistical evidence suggests that current vehicle restriction policies may inadvertently concentrate risk in specific time windows. These insights highlight the need for policymakers to refine urban mobility strategies by considering crash and traffic data simultaneously, implementing targeted public awareness campaigns, targeting speed enforcement, and incorporating enforcement dynamics into the design of vehicle restriction programs.