Authorities have increased freeway patrols and considered installing recorders on roadside traffic cameras.
Five people have been shot in their cars in apparently unrelated — and definitely unsolved — attacks. In at least three cases, the shooters were in other cars.
Manny Padilla, a California Highway Patrol chief in Southern California, said the bloodshed might reflect frustration with gridlock.
"Driving behavior has changed tremendously with all the congestion here. That causes people to be extremely short-tempered and inconsiderate," he said. "The courtesy we used to extend often isn't there anymore."