The dog is trying to protect you (it thinks that that's its job and doesn't know that approaching cars are not a threat). You have to train your dog to do what you want it to do instead of what it does instinctively (you can't train all the instincts out of a dog but you can teach it quite a lot - Rottweilers actually respond well to training, they're quite smart).
What I do is that every time my dog barks, I get up from what I'm doing and investigate (it's annoying but I believe that it's my responsibility not to just let it bark indiscriminately). I'm trying to teach her that I don't want her to bark all the time but not never (sometimes it's appropriate). Maybe for your neighbors' sake let the dog sleep inside until you can train it not to bark so much.
I love dogs, and I have one myself, but I hate it when dogs bark while I'm trying to sleep (in fact I hate it when I'm awake too). However, I don't blame the dogs, I blame their human handlers for not being responsible and controlling the dog's behavior better.