Rakha, H., A. Flintsch, M. Arafeh, G. Abdel-Salam, D. Dua and M. Abbas, Access Control Design on Highway Interchanges, Virginia Polytechnic Institute and State University, Blacksburg, Virginia Department of Transportation, Virginia Transportation Research Council (2008)
The report developed a methodology to evaluate the safety impact of different access road spacing standards in the vicinity of interchanges. Models were developed to compute the crash rate associated with alternative access spacing from a freeway ramp. The results demonstrated an eight-fold decrease in the crash rate when the access road spacing increases from 0 to 300m (1000ft). Furthermore, the crash rate reduced by 50 percent following an increase in the minimum spacing from 90m (300ft) to 180m (600ft).
Tables were developed from the models to quantify the impact of access and intersection spacing relative to freeway ramps on the expected number of crashes per unit distance. The tables showed an inverse relationship between crash rate and access road spacing.
Figure 5. Safety impact of access and intersection spacing relative to freeway ramps.
The study computed the safety cost of alternative access road spacing using a weighted average crash cost. Lookup tables were developed which can be used in the consideration of different access management regulations.
Figure 6. Crash costs of various access road spacings from interchanges.