During the winter months, San Joaquin, Stanislaus and Merced Counties are plagued by extremely dense fog which poses a severe hazard to drivers. Typically the fog season begins during the month of November and continues through February. Despite this predictable seasonal occurrence, multi-vehicle accidents are commonplace due to the combination of fog, excessive speeds and traffic congestion.
In an effort to enhance the safety of the motoring public, the California Department of Transportation implemented what is now known as Caltrans Advanced Warning System. The CAWS consists of 37 Changeable Message Signs, 30 weather stations and 124 speed monitor locations along Interstate 5 and State Route 12, 99, 120, and 580.
The CAWS system is fully automated; visibility sensors provide reduced visibility information and the speed monitors detect slow and stopped traffic. Working together, these components provide the data necessary to display the appropriate message on the CMS. "Low Visibility Conditions Reduce Speed" and "Slow Traffic Ahead" are only two of the helpful and informative messages displayed for motorists.
As resources allow, the California Highway Patrol has implemented "pace" units that work on major the highways between Modesto and Merced on foggy days when visibility is less than 500 feet. The CHP "pace" unit's slow vehicles to a safe speed during limited visibility conditions.
Caltrans and CHP are committed to enhancing the safety of the state highway system; however, it is a partnership effort. Motorists using the highway system need to follow the necessary precautions when driving with limited visibility or on wet roadways:
• Reduce vehicle speed;
• Drive with headlights on low beam. It is illegal to drive with just your parking or fog lights;
• Avoid crossing traffic unless absolutely necessary;
• Listen for traffic you cannot see;
• Use wipers and defroster as necessary for maximum vision;
• Be patient! Don't pass lines of traffic;
• Unless absolutely necessary don't stop on any freeway or other heavily traveled road;
• Consider postponing your trip until the fog clears;
• Normal speeds on dry roads can be deadly when driving on wet roadways;
• Observe the basic speed law and adjust your speed to match the conditions;
• Be sure tires have plenty of tread and are properly inflated;
•Wiper blades and defrosters need to be in good working condition;
• When slowing or stopping, gently apply the brakes;
• Drive with headlights on;
• Wet brakes can affect braking efficiency;
• Constantly be alert for signs of hydroplaning.