When it comes to cars for modern video games, because they don't use normal maps, they are more liberal with the polycounts. These are from one of the lastest Need for Speed games http://i.imgur.com/lZ7Egq3.jpg http://i.imgur.com/nDCTG23.jpg 100k tris for a car is not unheard of, though I'd aim for 30k to 50k.
I think a good thing to keep in mind is file size. My 2k maps are 12MB and my 59k models are 9.5MB in .obj format or 2MB in .fbx. What that means is that maps are significantly more expensive than polys, and since vehicles are usually monochromatic, it's often more efficient to allow them a dense polycount than the…