A time of day analysis of crashes involving large trucks in urban areas

• Large truck-involved crashes should be analyzed by time of day based on similar characteristics (i.e., traffic volume, driver behavior and light conditions).
• Five mixed logit models were developed for five time periods (12–4 a.m., 5–9 a.m., 10 a.m.–3 p.m., 4–8 p.m. and 9–11 p.m.) to identify contributing factors to injury severity.
• Key differences among the five crash severity models include traffic flow, light conditions, surface conditions, time of year and percentage of trucks on the road.

Previous studies have looked at different factors that contribute to large truck-involved crashes, however a detailed analysis considering the specific effects of time of day is lacking. Using the Crash Records Information System (CRIS) database in Texas, large truck-involved crashes occurring on urban freeways between 2006 and 2010 were separated into five time periods (i.e., early morning, morning, mid-day, afternoon and evening). A series of log likelihood ratio tests were conducted to validate that five separate random parameters logit models by time of day were warranted. The outcomes of each time of day model show major differences in both the combination of variables included in each model and the magnitude of impact of those variables. These differences show that the different time periods do in fact have different contributing factors to each injury severity further highlighting the importance of examining crashes based on time of day. Traffic flow, light conditions, surface conditions, time of year and percentage of trucks on the road were found as key differences between the time periods.