"You can make them look like a car, but cannot name them that car.
A good example of this is the Burnout, and GTA series.
Brands do not want games to crash model their cars. It looks bad. Look at the mess some of the cars end up in during a GTA session !
GTA gets around this by bending the brand a little. Audi becomes Obey."
Makes a great point.
The infringement comes in my opinion when the model is copied from another game and not the use of the model itself.