When the ship's going down is probably not the best time to teach lifeboat drills! Similarly, the best time to teach a dog not to chase cars is not when he is streaking off down the road in hot pursuit of a Mac truck. The best time to teach a dog not to kill chickens is before he kills one, not after.
We humans tend to have a problem with putting the dog into a situation where he is likely to make a mistake, just so we can correct him and teach him something. We think of setting the dog up like this as some form of entrapment, which goes against our sense of fair play. Fear not! Luckily, the dog doesn't deal with moral issues quite the same as we do and won't hold a grudge against you forever. At least, not if the training is done properly.
Take him on leash to a well-traveled road. Let him watch cars going by. If he shows any inclination to chase, correct him with the leash. Teach him to get off the road and into the ditch when a vehicle approaches. Think of it as preventing accidents and saving lives, both animal and human.
If you live in an area where your dog might chase livestock or steal chickens, take him into the area on ten or fifteen feet of line and give him the opportunity to start his chase. Just make sure he's brought up short by the line before he can actually achieve his goal.
Your dog will likely learn these lessons in one or two trials, but don't stop there. Keep taking him back to the distraction until it seems impossible to tempt him into making a mistake.
Good luck with your training!
Neil