Four of the five zombie types are easy to kill with a vehicle. Just some notes to keep in mind:
For the Feral Zombie - Yellowish zombie that leaps around with crazy hair - he's quick and can get out of the way pretty easily, so watch where you're driving, don't end up falling in a ravine and getting stuck or flipping your vehicle.
For the Armored Zombie (SWAT or Army) and Screamer, nothing to it, once you find them, run 'em down. The SWAT Zombie can be found randomly wandering around, easy to recognize by the helmet and the larger red circle on the map. Screamers are always found in and around infestations. They have no arms, and scream if you get too close.
For the Bloater - Make sure you have extra medicine on hand, because you'll need it to counteract the poison. Also make sure you have a medical facility in your home, because you'll probably get sick from it. And get out of the vehicle as soon as it is dead, to minimize exposure to the toxic fumes. The bloater has a fat neck and a nasty bloated gut, can't miss it.
For the Juggernaut - The huge Juggernaut can be tough. Hit the Juggernaut in reverse, with a pickup truck, don't ram it head on. Hitting it in reverse will wreck your back tires, but will not damage your engine at all, so even if you don't have a mechanic shop to fix it, at least you can drive home. Three good solid hits in reverse should take care of it. And like Pure Pip Raptor says in the comments, if it doesn't kill the Juggernaut outright, when he falls down, drive over him, and that will kill him.
Basically, if you play the game long enough, you'll have plenty of chances to see them and hopefully run them all down.