Good neighbors for 13 years deserve courtesy. They have every right to have a dog run loose on their property, whether it's roaming close to your property or not. Now, if it's actually coming on to your property (which it most likely will eventually, since it doesn't know boundary lines), then it's in your hands. But if I have good neighbors, I'm not going to shoot their dog unless I see it going after my birds.
I would speak with them out of concern for the dog almost getting hit in the road, and hopefully they'll restrict him. If you're willing to go the extra mile, you might even ask them to bring the dog over on a leash to see how he does around your birds, and to correct him if he goes after them so that he learns to stay away. That's what I did with my SIL's dog, and now that dog pays no attention to my chickens when she's here.
Maybe he won't learn, and more severe actions will have to occur if he goes after your chickens down the road. But maybe it will help, you won't have to shoot a dog, and you'll preserve a long time neighbor relationship.