In Tennessee, a low visibility warning system installed on I-75 dramatically reduced fog-related crashes.

May 2003
Interstate 75 and Tennessee 163,Tennessee,United States

Summary Information

This report, Best Practices for Road Weather Management: Version 2, contains 30 case studies of systems in 21 states that improve roadway operations under inclement weather conditions. The focus of this benefit is the low visibility warning system implemented in Tennessee in 1994. The Tennessee Department of Transportation (TDOT) and the Tennessee Department of Safety (TDS) deployed the low visibility warning system to control traffic during foggy conditions and close the freeway if necessary on Interstate 75 in southeastern Tennessee.

Managers with TDOT and TDS employed both advisory and control strategies to implement the warning system. Advisory strategies provide information on prevailing and predicted conditions and control strategies alter the state of roadway devices to permit or restrict traffic flow and regulate roadway capacity. TDOT installed environmental sensor stations, visibility sensors, and vehicle detectors; and used static signs with flashing beacons, variable speed limit signs, dynamic message signs, and highway advisory radio to notify motorists.

The low visibility warning system implementing a variable speed limit system has dramatically reduced crashes. While there had been over 200 crashes, 130 injuries, and 18 fatalities on this highway section since the interstate opened in 1973, by 2003, only one fog-related crash had occurred on the freeway since the system was installed in 1994.

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Best Practices for Road Weather Management: Version 2

Author: Goodwin, Lynette C.

Published By: U.S. DOT Road Weather Management Program, Federal Highway Administration

Prepared by Mitretek Systems for the U.S. DOT

Source Date: May 2003

EDL Number: 13828

Other Reference Number: Report No. FHWA-OP-03-081



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Goal Areas


Typical Deployment Locations

Rural Areas, Statewide


RWIS, ESS, Environmental Sensor Station, RWIS Station, road monitoring, weather station, environmental sensing station

Benefit ID: 2008-00531