Look into getting an invisible fence - I know people don't care for them (not humane etc..) but getting zapped a couple times is WAY better then getting hit by a car.
Friends of ours have lost 2 pups to cars on their street - they now have the invisible fence and a happy new pup.
(Maybe you can get a couple extra collars for the boys too!) Ok Ok just kidding - don't flame me!
Kim