Safety Impacts of Access Control Standards on Crossroads in the Vicinity of Highway Interchanges

Adequate spacing and design of access to crossroads in the vicinity of freeway ramps are critical in the safety and traffic operations of the freeway, crossroad, and properties near interchanges. Research attempted to develop a methodology to evaluate the safety impact of different access-road spacing standards. Results clearly demonstrate the shortcomings of the AASHTO standards and the benefits of enhancing these standards. The models developed as part of this research effort were used to compute the crash rate associated with alternative section spacing. The study demonstrates that the models satisfied the statistical requirements and provide reasonable crash estimates. Results demonstrate an eightfold decrease in the crash rate over an access-road spacing ranging from 0 to 300 m. An increase in the minimum spacing from 90 m (300 ft) to 180 m (600 ft) results in a 50% reduction in the crash rate. The developed models provide an excellent tool to evaluate the trade-off of alternative access-road spacing. Furthermore, the economic impacts of alternative access-road spacing can be computed by using a weighted average crash cost. This average crash cost can be multiplied by the expected number of crashes per kilometer to compute the cost associated with different access-spacing scenarios. It is anticipated that this procedure can assist policy makers in quantifying the trade-offs of different access management regulations.