We had a rat problem, only in and around the house, not in the vehicles. The Keys are infested with wood rats...they are protected down here. The only thing that worked was getting a couple cats. Now we have a cat problem...they weren't fixed til recently.
TxsGal's and Mikey's idea about the thing that makes noise sounds like the best option. The different scents normally work, but I think they get used to it.
Maybe some New York City residents can confirm this--I've heard that their sewer rats are so wild that even cats are afraid of them.
I haven't heard that about New York City, but I imagine some of them are pretty vicious and they often run in packs, so I can see cats being scared of them. I've heard in some places around the world, they are the size of cats...wouldn't want to come face to face with one of those.
The wood rats down here mostly do damage to the house, otherwise they seem fairly tame and run away if you approach them.