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 variable speed limit (VSL) and real-time warning (RTW) systems, which use real-time data to dynamically adjust speed limits and provide timely hazard alerts.

NCHRP Research Report 1176: Real-Time Warnings and Variable Speed Limits— Safety and Travel Reliability During Weather Events, produced by TRB’s National Cooperative Highway Research Program, is a guide designed to support transportation professionals in understanding, evaluating, and implementing these systems in response to adverse weather conditions. The strategies and case studies included in this guide are intended to help transportation agencies enhance roadway safety, improve traffic flow, and ensure drivers receive accurate, timely information to navigate hazardous conditions effectively.

The same project that produced NCHRP Research Report 1176 also documented its methodology and findings in NCHRP Web-Only Document 447: Evaluating the Impacts of Real-Time Warnings and Variable Speed Limits on Safety and Travel Reliability During Weather Events.

Infrastructure Assets: ITS
Resource Types: Research Report
Capabilities: Data & Information Systems, Tools & Technology
Management Processes: Monitoring & Adjustment, Performance Based Planning & Programming