Variable speed limit system site selection should be rigorous and incorporate analysis of existing speed profiles and roadway ingress/egress characteristics to assure proper spacing of VSL systems and sensor inputs.

An evaluation of variable speed limit (VSL) systems under a variety of operational conditions.

WB 1604; San Antonio; Texas; United States; NB IH-35; Temple; Texas; United States; IH-20; Ranger Hill; Texas; United States

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Lesson Learned

Primary lessons learned from the pilot tests included the following:
  • Use permanent equipment preferably mounted over travel lanes. Temporary equipment was not suitable for long-term operations.
  • Fully understand existing speed profiles and ingress/egress characteristics on the corridor. Assure proper spacing for VSL systems and adjustments to sensor inputs.
  • Plan for a large number of equipment and communications failures. Algorithms can be enhanced to address these issues and increase the public confidence in the messages posted by ensuring that they are correct and consistent. Test algorithm performance in shadow mode.
  • Consider the need to share real-time data with other agencies, such as the Department of Public Safety.
  • Conduct significant and on-going public outreach to assist drivers with understanding and complying with variable speed limits.

Based upon the data available for the VSL pilot program, VSLs would be beneficial if implemented to address inclement weather, congestion, or road construction.

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Evaluation of TxDOT Variable Speed Limit Pilot Projects: Final Report

Author: Kuhn, Beverly; Kevin Balke; Robery Brydia; LuAnn Theiss; Ioannis Tsapakis; Leonard Ruback; and Minh Le

Published By: Texas A&M Transportation Institute

Source Date: 06/01/2015

URL: http://d2dtl5nnlpfr0r.cloudfront.net/tti.tamu.edu/documents/TTI-2015-10.pdf

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Lesson ID: 2017-00780