If a dog is already prone to chasing cars, then it is best to seek assistance from a certified professional dog trainer who can help break the habit. According to the American Society for the Prevention of Cruelty to Animals, eliminating the behavior can be accomplished by keeping the dog on a short leash when walking, training the dog to come when called or associating the behavior with unpleasant consequences.
The effect of all of the previously stated deterrents are significantly maximized when assisted by a certified professional dog trainer, especially in the case of punishing a dog for chasing after cars. A dog trainer can provide feedback on the most reasonable, effective and humane ways to teach the dog that chasing cars is dangerous and not acceptable.
The ASPCA explains that some effective consequences include devices that make a loud or obnoxious noise, a repulsive spray or a device that inflicts some level of physical discomfort. Again, a certified dog trainer should be consulted when deciding on any of these techniques.
It is highly important that the dog is not given access to moving cars, and then physically hit when it proceeds to give chase. This may prevent the dog from chasing cars when the owner is present, but it does not change the behaviour. Additionally, a dog must not be allowed to begin running as fast as it can, and then stopped short when it has reached the end of the leash. This can cause serious physical injury and pain.