Real-Time Warnings & Variable Speed Limits
The recently released NCHRP Research Report 1176 Real-Time Warnings & Variable Speed Limits: Safety & Travel Reliability During Weather Events supports transportation professionals in understanding, evaluating, and implementing variable speed limit (VSL) and real-time warning (RTW) systems in response to adverse weather conditions.
Adverse weather conditions such as rain, snow, fog, and high winds pose significant challenges to roadway safety and mobility. These conditions not only increase the risk of crashes but also contribute to travel delays, congestion, and unpredictable driving behavior. To mitigate these risks, transportation agencies are increasingly deploying VSL and RTW systems, which use real-time data to dynamically adjust speed limits and provide timely hazard alerts.
The strategies and case studies included in this report are intended to help transportation agencies enhance roadway safety, improve traffic flow, and ensure drivers receive accurate, timely information to navigate hazardous conditions effectively.
Supplemental to this report is the NCHRP Web-Only Document 447 Evaluating the Impacts of Real-Time Warnings & Variable Speed Limits on Safety & Travel Reliability During Weather Events, which documents the report's methodology and findings.
Who is NCHRP?
The National Cooperative Highway Research Program conducts research in problem areas that affect highway planning, design, construction, operation, and maintenance in the United States.
Administered under the Transportation Research Board (TRB), NCHRP is a collaborative effort between the Federal Highway Administration (FHWA) and the National Academy of Sciences.
