In addition to all the ideas of ties and fences, why not try to stop his love of chasing and racing cars?

All 3 dogs we had when I was growing up, my Dad taught them to run AWAY from moving cars. He went out in the yard with the dog and a spare tire. PGet one with NO rim in it. Roll the tire at the dog. TRY to hit him. I know, it sounds terrible. I was a young girl and I used to run in the house crying to mom. When I was older, I asked Dad about it. He said the tire never had much momentum or power behind it from his roll. If it hit the pup, it was just going to stop and fall over. besides, Dad said, if it missed the pup, HE didn't want to be running all over the yard to catch up with it and try again!

The dog / pup may have a sore spot for a few hours, or a day (wonder if they turn black and blue under all that fur?), but it was just a slight bruise, it resolved quicky, and the dog learned the "hard" way to avoid vehicles.

Of course, the hardest way to learn may be fatal!

Good luck with you dog!