The Travel Aid system was designed to transmit suggested speed limits and advisory messages to in-vehicle units and dynamic message signs (DMS) through the Snoqualmie Pass area of I-90 east of Seattle, Washington. This 40-mile section of freeway experiences increased crash rates during the winter months because of snow, ice, fog, and other adverse weather conditions. The goal of this project, which began in 1992, was to reduce the frequency and severity of crashes through the Snoqualmie Pass.
To generate the suggested speed limits, road weather data were collected from radar vehicle detectors, roadside sensors, and environmental sensor stations and entered into an algorithm embedded within the Travel Aid operating system software. The information was processed in a central Travel Aid server located in a WSDOT project office. A Travel Aid operator then reviewed the suggested speed limit. If the operator deemed the suggestion appropriate, it was transmitted, along with traveler advisory messages, to the DMS.
This lesson is based on findings from the Travel Aid Evaluation Report completed by Booz-Allen and Hamilton in March 1999, with additional input from WSDOT staff involved in the project.
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