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FHWA Highway Safety Programs

Guidelines for the Use of Variable Speed Limit Systems in Wet Weather

fhwasa12022.pdf (2.08 MB)

FHWA Safety Program


August 24, 2012

1. Report No.


2. Government Accession No.

3. Recipient's Catalog No.

4. Title and Subtitle

Guidelines for the Use of Variable Speed Limit Systems in Wet Weather

5. Report Date

August 24, 2012

6. Performing Organization Code


7. Author(s)

Bryan Katz, Cara O'Donnell, Kelly Donoughe, Jennifer Atkinson (SAIC)
Melisa Finley, Kevin Balke, Beverly Kuhn (TTI)
Davey Warren (Brudis and Associates)

8. Performing Organization Report No.

9. Performing Organization Name and Address

Science Applications International Corporation
8301 Greensboro Drive
McLean, VA 22101

10. Work Unit No. (TRAIS)


11. Contract or Grant No.


12. Sponsoring Agency Name and Address

Federal Highway Administration
U.S. Department of Transportation
Office of Safety
1200 New Jersey Avenue, SE
Washington, DC 20590

13. Type of Report and Period Covered


14. Sponsoring Agency Code


15. Supplementary Notes

FHWA Project Leader – Guan Xu
FHWA Technical Reviewers – Richard Knoblauch, Ed Rice, Roemer Alfelor

16. Abstract

This report provides guidance on the use of variable speed limit (VSL) systems in wet weather at locations where the operating speed exceeds the design speed and the stopping distance exceeds the available sight distance. The use of VSLs during inclement weather or other less than ideal conditions can improve safety by decreasing the risks associated with traveling at speeds that are higher than appropriate for the conditions. By using VSLs, agencies can take into account traffic volume, operating speeds, weather information, sight distance, and roadway surface condition when posting speed limits.

This report provides guidelines for the design, installation, operation, maintenance, and enforcement of wet weather VSL systems. The guidelines presented in this report are intended for a broad range of audiences, from the transportation policy professionals who are considering whether or not their agency should use VSL systems to the engineers who are actually designing VSL systems for their jurisdictions. The information within this guidebook should be useful to anyone considering the implementation or development of a VSL system. This document also provides examples of the challenges, obstacles and issues that organizations have encountered when implementing VSL systems so that future implementers can develop practices that will increase their likelihood of success.

17. Key Words

Variable Speed Limits, Wet Weather, Roadway Conditions, Pavement Conditions, Visibility, Sight Distance, Traffic Management Center

18. Distribution Statement

No restrictions. This document is available to the public from: The National Technical Information Service, Springfield, VA 22161.

19. Security Classification (of this report)


20. Security Classification (of this page)


21. No of Pages


22. Price


Form DOT F 1700.7 (8-72)

Reproduction of completed page authorized.