From Halopedia, the Halo wiki
Civilian vehicles were cars, starships, aircraft, or boats used by civilians and designed to perform in a non-military combat capacity. Civilian security forces use their own types of vehicles. Civilian companies like the Liang-Dortmund Corporation as well have their own fleet of vehicles, some of which were paramilitary vehicles.
Automobiles on a number of planets used a mounted identification system. On Reach this is achieved through a barcode, while those on Earth use letters and numbers. Some automobiles on Tribute use a hybrid letter/number and barcode system.
Civilian variants of military automobiles
Other motorized vehicles
Covenant civilian vehicles
Civilian vehicles generally appear as scenery objects in Campaign and Multiplayer of various Halo games. In Halo: Spartan Strike, it is noted that when Grizzly tank or Wraith Tank runs over an intact vehicle, the armor will suffer minuscule damage. Destroying the vehicle before running it over is recommended to maintain a high score.
In Halo: Reach, a number of civilian vehicles are actually drivable. This includes the Cart, the S-2 Traxus Cargo Transporter, the Spade, and the HC1500. None of them have weapons and are quite easily destroyed. However the Spade actually allows Jorge-052 to stand on the rear platform and mount his chaingun to the roof.
A number of civilian vehicles appear as Forge objects. In Halo 3, two vehicles appear as placable scenery items. In Halo 5: Guardians, three vehicles are forge objects; the Fossa, the Dewmax, and an unnamed truck.