Another two people have been injured in a spate of deadly violence that has already claimed four lives on southern California highways.

Police in the Los Angeles area are investigating a number of freeway shootings, the latest of which left two young drivers wounded on the side of the road.

The Los Angeles Police Department says a bullet hit a car on Monday, the day after a 19-year-old man was shot three times as he drove on one of the city's many freeways.

Though wounded, the driver managed to pull his vehicle to the side of the road where he waved down a passing firefighter.

Early Saturday morning, a 16-year-old driver was shot three times by someone who pulled alongside his car as he and a 17-year-old passenger sped along Interstate 5.

The victim was able to drive himself to hospital.

In a statement, police said events leading up to that shooting indicate it may have been spurred by road rage.

In the past five weeks, two men were killed in separate shootings on Interstate 110. Another two people were shot and killed on freeways in neighbouring counties.

Police say the incidents, which are not new to the roads of Southern California, are not believed to be related.

So far this year, L.A. police have recorded 11 shootings on the highways. In 2004, a total of 36 freeway-shootings left one person dead. That was three fewer fatalities than the year before.

Now famous for its gridlock, Los Angeles was, in the 1980s, notorious for highway gunplay.