The National Academies

NCHRP 03-142 [Active]

Evaluating the Impacts of Real-Time Warnings and Variable Speed Limits on Safety and Travel Reliability during Weather Events

  Project Data
Funds: $400,000
Staff Responsibility: C. Crichton-Sumners
Research Agency: University of Connecticut
Principal Investigator: Dr. John Ivan
Effective Date: 8/4/2022
Completion Date: 8/4/2025
Comments: Research in progress.



Road Weather Management (RWM) has advanced significantly with new sources of road weather data and greater opportunities for more active management of roadways through direct communication with drivers. Pilot RWM applications and strategies have proven effective during weather events. Actively managing the system using variable speed limits (VSL) and real-time motorist warnings (RTW) based upon real-time weather and road condition data have proven to be effective strategies. However, additional research is needed to advance the practice and application of VSL and RTW nationally.


Because the effectiveness of these solutions depends on driver behavior, infrastructure owner operators (IOO) must understand the operational environment and the anticipated responses of drivers. For either VSL or RTW to be effective, the IOOs must know the current and anticipated environmental conditions, understand their impacts on mobility and safety, and formulate effective traffic management strategies to alert drivers. IOOs must understand how drivers receive VSL and RTW messages; interpret and integrate these messages with their own observations of roadway conditions; and react during different types of weather events. IOO’s must also understand the best ways to capture drivers’ attention; learn whether drivers respond differently to advisory or regulatory messaging; and understand the influence of other human factors and driver behaviors. Consistent and effective messaging would help IOOs achieve safer, more reliable transportation during adverse weather.




The objectives of this research are to (1) identify strategies and information needed to formulate effective messaging (including VSL and RTW) to elicit appropriate driver behavior and aid highway safety and mobility; (2) describe how to convey messaging with consideration of message locations, content, platform, and timing; and (3) identify the means to determine the effectiveness of the deployment of real-time messaging, including VSL and RTW, on safety and travel reliability.






Task 1.  Conduct a literature review related to real-time weather messaging including any previous research and pilot projects focused on driver behavior.


Task 2.  Describe the state of practice and identify successful practices and challenges encountered by state transportation agencies using road weather related VSL and RTW.


Task 3. Prepare a technical report that documents the work completed in Tasks 1 and 2. Include a detailed work plan for Phase II.




Task 4. Identify factors that improve practitioners’ understanding of driver perception, acceptance, and behavior associated with road weather related VSL and RTW in various scenarios.


Task 5. Identify strategies and information needed to formulate effective messaging, including VSL and RTW, to elicit appropriate driver behavior and improve highway safety and mobility.


Task 6. Describe how to effectively convey messaging with consideration of message locations, content, platform, and timing.


Task 7. Identify practical, applicable performance measures to assess the effectiveness of road weather related VSL and RTW deployments.


Task 8. Develop a practitioner’s guide that describes strategies, institutional roles and responsibilities, and operational considerations for the effective implementation of VSL and RTW for weather management.


Task 9. Develop a final report that at a minimum includes (1) an assessment of the current state of practice; (2) the requirements necessary to support real-time weather messaging needs; and 3) guidance for state departments of transportation (DOT) officials to plan and design a system that can be efficiently and effectively maintained.


STATUS: Research in progress.


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