Unfortunately, sometimes you have to do that. If you really feel bad about it, drive on over and confront the owner. It's not the dogs fault, it never is. It's the pet owners responsibility, by law, to keep the dog out of the road, and away from moving vehicles. If they can't control their pet, then they have no business having one.

I've confronted people several times on this subject. Usually it's just someone who is irresponsible and doesn't realize, they just wanted a dog for a pet. Once you lay down the law with them, they'll usually make an attempt to control the dog.