Well, I feel like if I were driving a 1500 model truck or heavier duty, moving through a decent sized horde wouldn't be impossible. Especially with 4x4. However if you're driving a car with lower clearance in the suspension and a 4 cylinder motor like a Honda (or like a few models of in game cars,) you wouldn't be able to run a lot of zeds over without getting stuck or inflicting serious damage to the vehicle. I do feel like hitting a body at high speed no matter what you're driving is going to do a lot worse than crack your head light like I've experienced in game.
