Evaluation of Variable Speed Limit Pilot Projects for Texas Department of Transportation

摘要

In May 2013, the regular session of the 83rd Texas State Legislature passed House Bill (HB) 2204 related to the establishment of a variable speed limits (VSL) pilot program by the Texas Transportation Commission. The bill was signed into law by the governor in June 2013. In December 2013, the Texas Transportation Commission established Rule §25.27 of the Texas Administrative Code authorizing and requiring the Texas Department of Transportation (TxDOT) to implement a variable speed limit pilot program to “study the effectiveness of temporarily lowering prima facie speed limits to address inclement weather, congestion, road construction, or any other condition that affects the safe and orderly movement of traffic on a roadway.” The goal of the pilot program was to deploy VSL in up to three locations to test the concept under three operational conditions and to determine the impacts of VSL on facility operations and safety. The specific objectives of the pilot project evaluation were to determine how much congestion was reduced in the area impacted by the implementation of VSL, to understand the users’ perceptions of the VSL systems, to assess the safety impacts of VSL, and to determine the overall costs and benefits of VSLs. Up until this point in time, VSL was not a legal alternative for freeway operations in Texas. After the bill was passed, TxDOT worked with the Texas A&M Transportation Institute (TTI) in selecting pilot project sites for the development, implementation, and evaluation of VSL. The VSL systems were to be used for the purpose of controlling speeds at sites that have (a) construction work zones, (b) weather-related events, and (c) urban congestion. This paper presents the overall approach to the development, implementation, and operation of the VSL pilot projects along with the analysis of the installations with respect to their impact on congestion, safety, users’ perception, violations, and benefit-cost of the projects. It also presents a number of lessons learned throughout the course of the pilot tests that provide beneficial insight into how to improve similar projects for permanent installations. Based upon the limited data available for the VSL pilot project, it was determined that VSLs would be beneficial if implemented to address inclement weather, congestion or road construction. VSLs had a safety benefit at each location and motorists had a clear understanding of the purpose of the VSLs.