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21st Century Operations Using 21st Century Technologies

Synthesis of Variable Speed Limit Signs

Technical Report Documentation Form

1. Report No.


2. Government Accession No.

3. Recipient's Catalog No.

4. Title and Subtitle

Synthesis of Variable Speed Limit Signs

5. Report Date

May 2017

6. Performing Organization Code

7. Author(s)

Bryan Katz, Jiaqi Ma, Heather Rigdon, Kayla Sykes, Zhitong Huang, Kelli Raboy

8. Performing Organization Report No.

9. Performing Organization Name and Address

11251 Roger Bacon Dr.
Reston, VA 20190

ToXcel, LLC
7140 Heritage Village Plaza
Gainesville, VA 20155

10. Work Unit No. (TRAIS)

11. Contract or Grant No.

DTFH61-12-D-00045, Task T-5009

12. Sponsoring Agency Name and Address

United States Department of Transportation
Federal Highway Administration
1200 New Jersey Avenue, SE
Washington, DC 20590

13. Type of Report and Period Covered

Research Synthesis, March 2016-December 2016

14. Sponsoring Agency Code


15. Supplementary Notes

Jimmy Chu, HOTM, Government Task Manager (GTM)

16. Abstract

Variable speed limit (VSL) systems utilize information on traffic speed, occupancy, and volume detection, weather, and road surface conditions to determine the appropriate speeds at which drivers should be traveling, given current roadway and traffic conditions. The use of VSL during less than ideal conditions, such as traffic and weather conditions, can improve safety by decreasing the risks associated with traveling at speeds that are higher than appropriate for the conditions and by reducing speed variance in traffic. In addition, VSL can be used to dynamically manage speeds during planned (rush hour congestion) and unplanned (incidents) events. Used in conjunction with managed lanes and other active traffic management (ATM) strategies, VSL can respond to downstream congestion to eliminate or delay bottlenecks and mitigate the possibility of crashes.

Based on a comprehensive literature review along with agency interviews to gather information on existing, deactivated and planned VSL systems, this synthesis provides a comprehensive review of current practices on VSL operations, particularly experiences from deployments in the U.S., and to identify successful and best practices from the following perspectives: planning and policy, design, deployment, and standards, operations and maintenance, and outcomes.

17. Key Words

Variable speed limit (VSL); planning and policy; design; deployment; standards; operations and maintenance; active traffic management (ATM)

18. Distribution Statement

No restrictions.

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.

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