Road Weather Management Program
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Best Practices for Road Weather Management Version 2.0


I-68 Reduced Visibility Fog Detection and Warning System: Evaluation Report


This report describes the evaluation of the "Reduced Visibility" warning system on I-68 in Garrett and Allegany Counties in western Maryland. The system uses "Reduced Visibility Possible" signs located in two fog-prone areas, one near Big Savage Mountain and the other near Keysers Ridge. The Evaluation Plan had three specific objectives: (1) to evaluatemotorists' response to the "Reduced Visibility" sign; (2) to evaluate the system's response based on its concept design; and, (3) to evaluate the system's operation, including all components such as the fog sensor, radio equipment, sign and flashing mechanism and communications interface. Overall, the system must be considered a success in the sense that it detects fog when fog is present and provides the relevant information to drivers on I-68 via the sign message. With respect to the operation of the system itself; this was clearly a success as the components (fog sensors, RWIS logic, radio communications, and the sign itself) all operated as designed. Positive feedback from road users has indicated that the motoring public perceives the system as a useful resource.


Sabra, Wang and Associates, prepared for the Maryland State Highway Administration

Date: 2006


Sabra, Wang & Associates


Motorist warning system
Environmental Sensor Station (ESS)
Traveler information

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