Applying Variable Speed Limits and the Potential for Crash Migration

Variable speed limits (VSL) were applied on I-4 in Orlando, Florida, through microsimulation to reduce crash likelihood. VSL application improved safety by simultaneously implementing lower speed limits upstream and higher speed limits downstream of the location where crash likelihood was observed in real time. Real-time crash likelihood was calculated with the use of models developed in previous research. The improvement was realized in the case of medium- to high-speed regimes on the freeway, but no benefit was achieved in low-speed situations; that is, there was no substantial safety benefit from applying VSL in congested situations. In addition to the safety benefit, travel time was also reduced. The simulation results showed a potential for crash migration. The crash potential appeared to relocate to a location downstream of the detector of interest. Upstream, little change occurred, except at the location where the change in speed took place. While there are some crash migration effects, the overall safety of the freeway was improved due to VSL application.