Variable Speed Limits

Variable speed limits are speed limits that change based on road, traffic, and weather conditions. Variable speed limits offer considerable promise in restoring the credibility of speed limits and improving safety by restricting speeds during adverse conditions.

• Guidelines for the Use of Variable Speed Limit Systems in Wet Weather
• Examples of Variable Speed Limit Applications [PPT 237 KB]
• Legal Research Digest No. 47: Judicial Enforcement of Variable Speed Limits [PDF 485 KB]
• Variable Speed Limits Presentation [PPT 5.32 MB]
• Managing Speed in Work Zones: Variable Speed Limit Systems Paper Presentation [HTML, PPT 1.3 MB]
• Safe Speeds in Work Zones Leaflet [HTML, PDF 481 KB]
• Field Operational Tests of VSL in Work Zone

Field Operational Tests On Variable Speed Limits In Work Zones

Field tests are being carried out in cooperation with Maryland and Michigan to implement and analyze the effectiveness of variable speed limits (VSL) in work zones. These projects are a joint effort between Safety and ITS Joint Project Office. The VSL are displayed on portable trailers and rely on input of vehicle speeds, presence of road work activity, and other information to post an appropriate speed limit, allowing motorists to maintain the most efficient and safe speeds, without endangering themselves, other drivers, or workers.

Results of several deployments in an 18-mi work zone in Michigan are now available [PDF - 159 KB]. Field trials of variable speed limits in a Maryland work zone are planned to begin in December 2005. A synthesis report of the results and lessons learned from the tests will be distributed to all states, so best practices for safe and efficient travel through works zones can be applied.