They are orange industrial carts and green security carts scattered in the underground tunnels, as well as in South Plaza and in front of the Fortune City Hotel. The industrial carts can kill up to 200 zombies and the security carts can kill up to 150 zombies before exploding, unless the player crashes, in which case the possible kill count is lowered.
The orange carts can hold one passenger along with the driver, while the security carts with lights on top have two more seats in the back, allowing a total of three passengers and the driver to use the cart.
Its durability can be increased with the Driving magazine.
The 4x4 has two names in the PC game file items.txt, "IndustrialCart" and "SecurityCart". They are actually two different distinct vehicles; one is not a sub-vehicle of another. There is also the Postal Cart, another separate entry, which is only seen in Mail Order Zombrex, that, although it cannot be driven in the game, is set up to be driven in the PC files.
The only differences between the three vehicles: