In what we see in the game? The Gamebyro/Creation Engine shits itself when it has to do anything like that. Also the scale of the map is so condensed that it wouldn't make very much sense to have it. I know the guys working on The Frontier put together some vehicles, which look pretty fair as far as modders go. But I know Bethesda would be a little anal about the way the vehicles work. I just don't think the game can support things like that.
One thing I would like to see - even if it will probably never happen - is a return to/a fusion of the system in Fallouts 1 and 2. A theoretically large game world, with individual cells representing towns and cities in a proper scale. Sure, it would remove the "wandering the wastes" thing, but in reality how many people actually do this? I feel like most people, after a first run through, are going to fast travel. Random encounters and such can be dealt with like in the originals. I feel like this system would allow for vehicles (obviously) and for a better sense of scale of communities in the game.
A man can dream.