This study was conducted to investigate the relationship between congestion and accidents with a specific emphasis on the impact of traffic volume levels on accident frequency, rate, and severity. The accident data from five freeways (I-495, I-695, I-95, I-270, and US50) and five arterials (MD2, MD355, US1, MD410, and MD97) were analyzed with multivariate statistical methods to evaluate the widespread belief among traffic safety professionals that an increase in congestion levels often results in more, but less severe, accidents on freeways and/or local arterials. However, the impact of congestion on the accident rate tends to vary between freeways and arterials, and differs significantly across peak and off-peak periods. The estimation results, based on the available sample data, reveal that accident rates on local arterials tend to decrease with an increase in traffic volume. In contrast, accident rates on freeway segments during peak hours indicate a positive correlation with traffic volume per lane. Additionally, freeway accident rates during off-peak periods appear to be random in nature, and not necessarily correlated to any specific factors.
Abstract