The National Academies

NCHRP 03-142 [Anticipated]

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

  Project Data
Source: AASHTO Committee on Transportation System Operations
Funds: $400,000
Staff Responsibility: Camille Crichton-Sumners
Fiscal Year: 2022

This project has been tentatively selected and a project statement (request for proposals) is expected to be available on this website. The problem statement below will be the starting point for a panel of experts to develop the project statement.

Road Weather Management (RWM) involves use of solutions and strategies that minimize the impact of weather events on transportation system operations to increase safety and travel reliability. It has advanced signifi-cantly with new sources of road weather data and the opportunity for more active management of roadways through various Transportation Systems Management and Operations (TSMO) deployments that enable more direct communication with drivers. As a result, during the past decade there has been growth and experimentation with RWM safety applications and strategies that have proven to yield high payoff benefits during weather events. A survey of TSMO practitioners conducted in 2019 revealed six strategies that would have the most positive impact on system safety and reliability during weather events. Actively managing the system using real-time data on the road conditions to provide variable speed limits (VSLs) and real-time motorist warnings (RTWs) for road weather hazards were both identified as high priority strategies. However, there is a need for additional research on the safety and travel reliability benefits as well as systems engineering processes to advance VSL and RTW for road weather. Notably, each of these solutions depend on actions by the driver, requiring a greater understanding of the related human factors in order to optimize the systems and measure the safety and travel reliability payoff of these strategies.

In order for VSL to be effective in changing driver behavior and increasing roadway safety and reliability, the infrastructure owner/operator (IOO) must have a detailed understanding of both the operational environment and the anticipated responses of drivers. In order for RTW to be effective, the IOO must know the current and antici-pated environmental conditions and have a mechanism at their disposal to alert drivers. As with VSL, the IOO should have a detailed understanding of how drivers will react to RTW during different weather events, how they receive and interface with the messages, whether they respond differently based on advisory or regulatory messag-ing, and many other human factors and driver behaviors. The IOO also needs to understand the ideal ways to cap-ture the driver’s attention to the message/warning and needs to have approved standards/consistent messaging to deliver.

In June 2019 a peer exchange identified several gaps in the existing body of knowledge connected to ef-fective VSL and RTW operation and the understanding of driver behavior. These include:
• Safety and travel reliability benefits.
• Baseline and document driver understanding of VSL and RTW.
• Detailing the current understanding of anticipated driver response and level of compliance to messages during all potential operating conditions.
• Documenting the effectiveness of different visual cues and messaging on driver response.
• Documenting the effectiveness of in-vehicle messages versus messages generated via roadside or over-head signage on driver response.
• Detailing the impact of other operating restrictions (e.g., commercial vehicle restrictions such as lane re-strictions and chain requirements) on driver response to messages.
• Understanding of the impacts of agency and partner regulatory and enforcement authority for viola-tions on driver behavior (including automated enforcement options).
• Investigating potential design modifications needed to account for human factors and driver behavior.

The objective of this research is to advance the RWM strategies of VSL and RTW that lead to safer and more reliable roadways through a better understanding of driver behavior. Specifically, this research aims to (1) provide a detailed understanding of the anticipated driver behavior impacts from VSL and RTW on safety and travel reliability; (2) identify and convey best practices in VSL and RTW messaging including message locations, content, platform, and timing; and (3) strengthen the ability of agencies to plan for and/or optimize VSL and RTW functions that maximize impacts on driver behavior for improved safety and travel reliability outcomes.

The anticipated products of this research will offer immediate benefit to IOOs dealing with roadway safety and travel reliability challenges due to weather. It will also promote the use of beneficial and cost-effective RWM strategies among state DOTs and other IOOs to increase network safety and security. 

Direction from the AASHTO Special Committee on Research & Innovation: Coordinate with an ongoing Transportation Pooled Fund project. Include consideration of return on investment in the scope of work. Consideration should be given to including pedestrians and cyclists within the right-of-way.


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