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

• Jul 24, 2020

Research Description

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 (VSL) and real-time motorist warnings (RTW) for road weather hazards were both identified as high priority strategies. At a TSMO focused peer exchange of State DOTs, FHWA, AASHTO, NOCoE, and a consultant held in June 2019, participants agreed that the use of VSL and RTW systems for weather applications is still advancing nationally, but that there is a need for additional research at the national level 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 or driver response, requiring a greater understanding of the human factors and driver behaviors involved in order to optimize the systems and measure the safety and travel reliability payoff of these strategies.

Many states including Ohio DOT (VSL on I-90 east of Cleveland) and Michigan (RTW signage for slippery roadways and bridges) have seen significant safety and reliability benefits (eliminating fatalities and serious injuries and reducing overall incidents) associated with these near real-time TSMO strategies.

Additional Supporting Information

VSL are systems that provide flexible speed limits for drivers, as opposed to the traditional fixed speed limit. VSLs allow an infrastructure owner-operator (IOO) to post speed restrictions—regulatory or advisory, depending on local policy—that are based on real-time information that may not be available to the motorists, such as congested conditions ahead, a major incident, or weather events such as fog or ice. Most VSL programs use roadside or overhead signage to notify motorists.

RTW can refer to any message or technology that improves traveler awareness of an inclement condition when that condition is present. In the RWM context, RTW generally refers to a notification provided to drivers of inclement weather conditions, usually consisting of a brief description of the condition and a recommended adjustment to their driving behavior (for example slow down, use caution, or stop and seek shelter followed by why you should). RTW can be distributed through a variety of mechanisms including roadside or overhead signage and radio transmissions. Some examples of RTW applications include icy curve, high water warnings, low visibility warnings (including snow, fog, and dust applications), high wind warnings, and evacuation guidance systems. To help influence driver behavior/attention/response, a message of action should be followed by a short succinct reason.

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Submitted By

Steven Cook

Michigan Department of Transportation

517-636-4094

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