Project Summary
Assessing the impact of raising truck speed limits on freeways has become an important issue, given the potential to increase economic productivity, and the associated safety concerns regarding higher speed limits. There is a recent discussion regarding whether truck operating speed has a significant influence on the frequency and severity of crashes on the freeway based on two speed limit policies: differential speed limit (DSL); and, uniform speed limit (USL). DSL policy sets lower maximum speed limits for buses and trucks, whereas USL policy sets uniform speed limits for all vehicles. California ascribes to DSL policy and sets the speed limit for trucks at 55 mph, compared to 65 mph for passenger cars. However, there is no compelling evidence to support the widespread application of DSL. Only a handful of States (California, Oregon, Washington, Idaho, Montana, Michigan, Indiana and Arkansas) practice this policy. This project will use statistical modeling to explore the tradeoff between safety and mobility for setting the truck speed limit on freeways. Additionally, this project will establish a safety index to inform decision makers of potential safety issues, capacity constraints, environmental effects, and economic aspects related to adjusting speed limits on California roadways. Moreover, a comparison will be drawn among different states that had raised truck speed limits (changed speed limit policy from DSL to USL) to evaluate the before and after effect of the speed limit changes. In addition to the incident datasets from California Highway Patrol (CHP) and other national data repositories (e.g. Fatality Analysis Reporting System), a drone will be used to record the short-term trajectory of the traffic of critical maneuvers (e.g. lane-changing, merging, diverging).
