Is there room for another vehicular combat game?

Yes, there's always room for more good games. Fortunately for you, the games you mentioned are pretty bad. Look up their ratings on BGG and you'll see what I mean: Battlecars (6.28), Car Wars (6.22), Thunder Road (6.18), RoadKill (5.89), Wreckage (5.72), Dark Future (5.85), and Car Wars: The Card Game (5.15). Most of the games I play are rated 7.00 or higher. The fact is that this really cool theme just can't make up for poor game play.

I think one of the keys would be to make a quick-to-play game with no plotted movement and very few variables. I think that the mechanism at the core of Cthulhu 500 (6.06) is a good one, but the game was ruined with an outlandish theme. Personally, I'm not a fan of Wings of War because of its imprecision (I've always preferred hex games to miniatures), but I'd be happy to entertain some ideas.

A 6+ is not a bad rating. Event the top game only gets an 8.33 out of 10. I would rather play Car Wars then Agricola on an average day.

If you think you can make something better of unique go for it.

I think there is plenty of room in this genre. So go for it.

Car wars strikes me as too much, It gets some love for being from a different era of games.

I think that thunder road is the best choice of those games.

The first choice you should make would be do you want free form movement like in wreckage or car wars. or track single direction movement, like formula de or thunder road.

Not for nothing, but personally I'd love to see a Vehicular combat game in an urban enviroment that has goals and quite possilby a team. Personally the most fun I've had with Vehicular combat has been in an RPG like shadowrun where I need to get my dude somewhere while being chased and trying not to crash. I'd love to see that translated to a quick and easy board game.