Although very dangerous behavior, car chasing is very rewarding for the dog. Dogs love to chase anything that runs, and the faster it runs, the better. To extinguish the behavior, you must negate the reward of the chase. Car chasing is most often done by dogs that have the run of the property and are not exposed to many cars.
Expose the dog to traffic by making a point to walk on busy streets occasionally. Command him to remain in a sit-stay as cars pass, and snap the collar back if he attempts to move. You can set the dog up for a car chasing correction by having a friend armed with several cans filled with rocks, for noise effect, drive up to or past the area where the dog starts chasing. Instruct the helper to put on the brakes as fast and noisily as possible when the dog is at a full chase. When the car comes to a screeching halt, have the helper jump out of the car and create enormous noise and chaos by throwing the cans near the dog.
If the dog is not likely to bite, have the helper aggressively chase him home, throwing cans behind him. Repeat the setup with different cars, and if possible, different people, until the dog refrains from chasing cars. You can also use the corrections for car chasing when a dog acquires the nasty, dangerous habit of chasing bikers, joggers, and horseback riders.