Relating Safety and Capacity on Urban Freeways

This research sought to investigate the relationship between capacity and safety on freeway roadways in New Jersey. Using the State's roadway database, capacity was estimated for State roadways using the procedures in the Highway Capacity Manual. Crash prediction models were developed relating crashes and crash rates to the geometric variables used to estimate capacity as well as to capacity and v/c ratio. The research showed that as capacity increases the number of crashes and crash rate also increases. As v/c ratio increased the number of crashes and crash rate decreased indicating that congestion may result in reduced speeds and as a result a lower number of crashes and crash rates. The research points to the need to include operational parameters in performing road safety evaluations.