Operational and Safety Effects of the I–95 Variable Speed Limit System in Fredericksburg, Virginia

About the report:

Variable speed limit (VSL) systems have been broadly deployed to address safety and mobility concerns both in the United States and internationally. In June 2022, the Virginia Department of Transportation (VDOT) activated a VSL system on I–95 northbound about halfway between Washington, D.C., and Richmond, VA. This section of I–95 experiences high traffic volumes and densities, resulting in significant delays and unreliable travel times. There are also a high number of congestion-related crashes and incidents. These problems are particularly prevalent on the weekends in the summer when recreational traffic volumes increase. While many past VSL deployments have attempted to address urban congestion or mitigate safety issues due to inclement weather, this deployment was unique in that it was intended to address traffic congestion created by this weekend traffic by encouraging more uniform speed selection, dampening the effects of shockwaves, and providing advance warning of congestion. Only traditional enforcement was performed on this corridor, and no targeted enforcement or automated speed enforcement was used. This report discusses the characteristics of the deployed system, as well as its safety and operational effects, using approximately 17 months of post-deployment data.

Results show that drivers responded to the VSLs, and that mean speeds and speed distributions changed during transitional flow states. Early safety results also showed reductions in crash severity. Travel time and reliability results showed mixed trends, with travel times and reliability generally improving on weekends, but sometimes worsening during the week as compared to the year prior to system activation. An annual benefit of approximately $2.57 million per year, primarily due to safety improvements, was determined, but this value is very preliminary and should be re-examined as additional data becomes available. This report recommends that VDOT and Virginia Transportation Research Council re-assess the system effects after 3 years of data become available and that the VDOT Traffic Operations Division assess whether other locations are likely to benefit from VSL installation.

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