Well, that was fun! I like how you included the popular camera modes in the game, and there's also a minimap.
Too bad there are no graphics for the surroudings, and I believe Unity has some default assets, like trees. Speaking of surroundings, also the walls don't damage the car! The game got way easier as soon as I noticed that.
The physics freak out at times. Sometimes I effortlessly run through the entire horde of zombies, and sometimes just one of them stops me while I'm at full speed.
Also, the horde spawns should check the player's position - I once lost almost the entire health, when a horde spawned right on me.