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Best Practices for Road Weather Management Version 2.0

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Title:

A Study of the Response of Highway Traffic to Dynamic Fog Warning and Speed Advisory Messages

Abstract:

This study examines the response of traffic to messages displayed by a Dynamic Message Sign (DMS) warning of fog ahead and advising specific speeds at progressively lower visibility levels. Over a two-year period of study, the speed, length and time of detection were individually recorded for all vehicles at four sites: two prior to exposure to the DMS, and two after exposure to the DMS. Mean speed, speed variance and a new metric, potential collision speed (PCS) were calculated. PCS is a predictor of the impact speed in a potential chain collision that considers visibility as well as the speed and separation between individual vehicles. There is little to no evidence that mean speed, speed standard deviation or PCS were influenced by the DMS messages. The exception may be for visibilities between 100 and 150 feet. Drivers appeared to respond predominantly to their own perceptions and reduced speed in fog, but not nearly enough to compensate for the reduced visibility distance. When advised to reduce speed to 30 mph in dense fog, mean speeds averaged 61 mph.

Source(s):

85th Transportation Research Board (TRB) Annual Meeting; California Polytechnic State University and Loragen Corporation. For an electronic copy of this resource, please direct your request to WeatherFeedback@dot.gov.

Date: 2006

Author:

MacCarley, Ackles, Watts

Keywords:


Speed
Motorist warning system
Dynamic Message Sign (DMS)
Driver behavior
Intelligent Transportation Systems (ITS)
Traveler information
Visibility

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