This exact thing happened to me last summer. Country road, it wasn't 3 am but it was nighttime. This dog was just standing in the road and didn't even get out of the way when I approached. I pulled over, turned on the flashers, and checked his collar. Called the number and the owner came out to pick him up.
Turns out he was one of two hunting dogs this guy owned. They were out taking a walk when they came across a coyote. The coyote bolted and the dogs both freaked out and ran away. He had been driving around for over an hour looking for them. Was so happy to know that at least one of them was safe.
You never know why a dog is out on its own. If it has identification, there's no excuse to not at least try to contact the owner. If that dog hadn't had ID, I'm not sure what I would have done. I wouldn't have been able to keep him at my place since we already have a dog and you can't just throw another one in the house like that. I guess if the dog was completely without a collar, I'd just let him go, but I'm not sure what the right thing would be to do in that situation.