Variable Speed Limits (VSL) display safe speeds for different travel conditions by adjusting posted speed limits based on real-time traffic, roadway, and/or weather conditions. VSL systems can present far more credible information (realistic speed limits) to the motorist, responding to both day-to-day changes in congestion as well as roadwork activity as motorists go through a given area. The goal of VSL is to harmonize the flow of vehicles to better manage congestion and reduce crashes due to speed differentials along the corridor. VSL deployments in other areas have been shown to reduce crashes by as much as 30 percent. It may sound counterintuitive, but reducing the travel speed can actually improve travel times and reliability during congested conditions.
First employed in 1960 along the Lodge Freeway in Michigan, VSL use in the U.S. has expanded to programs in many locations, several of which include hazard warnings related to traffic and/or weather conditions in addition to variable speed limits. Local motorists may be familiar with VSL systems that have been deployed on the New Jersey Turnpike and along I-495 in Delaware.
Along the entire 12-mile I-76 Corridor in Montgomery County, 72 VSL devices are being deployed to replace the existing 50/55 MPH static speed limit signs. Construction was completed in late 2020 and the VSL system is currently undergoing testing by PennDOT. VSL devices will be activated in Spring 2021 and provide static speed limits for a time while the automated system is further tested. The VSL signs will serve as enforceable, regulatory speed limits, not recommended speed advisories.