well..here is an easy button....move to a house not by a road! LOL
I joke because my dog does the same thing and when I was house hunting and found where I live now, my 1st thought was how great it would be for my dog cause we are waaaayyyy off the road.
In all seriousness...it is a hard thing to train a dog not to chase cars, afterall...they chase the car and the car goes away, mission accomplished. The dog feels rewarded every time it chases a car and the car disappears. The best way to train this away is to work on leash until they show no interest in chasing the cars or even looking at them as they go by. When you think you are ready to let it off leash, have a friend or relative drive a car by and see if the dog remains at ease. If the dog chases the car still, then you need to work on respect in general off leash, the dog must not think in a different fashion when it is off leash versus on leash. In that case a shock collar works good. Then the dog learns that it must listen even when a distance away. If you don't want to use a shock collar then you will need a really long rope and test the dogs listening skills at the end of the rope when the dog thinks it's far enough away not to listen. Keep in mind that when training a dog it is important to use positive reinforcement not negative reinforcement. acknowledge when the dog is being good, not when it is being bad. Good luck!
