About 7:25 a.m. on November 10, 1980, southbound traffic on Interstate Route 15 suddenly encountered dense fog north of the Highland Avenue offramp near San Bernardino, California, that reduced visibility to between zero and 50 feet. Drivers, whose vehicles were traveling 55 mph on the well-maintained, eight-lane, divided highway, said the visibility obscurement was immediate and unexpected. Some drivers slowed their vehicles partially as they entered the fogbank and others did not. A tractor-trailer combination vehicle braked suddenly to avoid a small car that changed lanes in front of it, and a pickup truck struck the trailer from the rear. This initiated a chain of collisions that involved at least 24 vehicles over a period of 5 to 10 minutes within a distance of 450 feet and resulted in 7 fatalities, 17 injuries, and extensive damage to all vehicles.