Visibility in a tule fog is typically less than an eighth of a mile; over a twenty year period, these fogs were responsible for more than 200 crashes, 130 injuries and 18 fatalities.

August 11, 2008

LINDON, UT—The California Department of Transportation is implementing an innovative fog warning system along a stretch of Highway 99 and has chosen to use SmartSensor HD to monitor the effectiveness of the system. 

The valleys of central California are plagued by tule fog, a dense ground fog that forms at night in late autumn and winter. Visibility in a tule fog is typically less than an eighth of a mile; over a twenty year period, these fogs were responsible for more than 200 crashes, 130 injuries and 18 fatalities.

The Caltrans system detects fog and displays a warning for drivers on variable message signs. By November 2008, as many as 70 SmartSensor HD units will be deployed along the highway to monitor traffic to determine if the warning system is working as intended. Caltrans selected HD because of its all-weather performance and its ability to accurately detect per vehicle speeds, which are critical in foggy conditions.