The decision to build a new interchange between an existing pair of interchanges is made by evaluating whether there is sufficient need for traffic to enter and/or exit the freeway at that location. The obvious intent is to reduce the systemwide travel times and delays for all users by providing convenient freeway access and egress. Although there are ways to evaluate these operational benefits quantitatively, to date researchers have not expressed in measurable terms the compromise in safety, or the increase in crashes per mile of freeway. This knowledge is essential for conducting a comprehensive cost-benefit analysis of new interchange construction projects. To fill this void, we endeavored to study interchange spacing from a safety perspective by estimating regression models to express crash frequencies as a function of highway characteristics, including interchange spacing. We then used the regression models to quantify the crash sensitivity to interchange spacing for fatal and injury crashes. We used data pertaining to freeway sections from 7 urban freeways in California and 10 urban areas in Washington for building the regression models. (Author/publisher)
Abstract