Tractor unit

A tractor unit, traction unit, road tractor or prime mover is a heavy-duty vehicle, usually with a powerful engine and several axles. The tractor unit serves as a method of moving trailers. Trailers can be swapped between tractor units quickly so the unit does not stand idle whilst the load is unloaded or loaded, unlike a rigid, and is not restricted to one type of goods as trailer types can be swapped e.g. Bulk tipper to a box van. The tractor-trailer combination also means that a load can be shared across many axles, yet be more maneuverable than a equivalently sized rigid truck. The tractor unit couples to the trailer using some sort of mechanical lock system, usually a fifth wheel. A tractor unit is primarily designated a freight vehicle and is most common in the heavy goods vehicle class of vehicles although smaller van based tractor units do exist.

A tractor unit was used a haul a trailer from an Insurrectionist bomb assembly factory to a diner on Tribute. The cabin was damaged as a round from a Model 99 Special Application Scoped Rifle punched through it, killing the driver. The trailer was later detonated by his accomplice, destroying the trailer, tractor unit, and diner, killing 38 civilians and three UNSC Marines.

Trivia

 * Tractor units appear in Halo 3, both in the campaign missions set on Earth, and in Forge. The game uses them as scenery however, since they do not count as drivable vehicles. Each tractor unit costs $8, and only two can be placed per map.
 * Tractor units, sometimes linked to their trailers, appear as scenery objects in Halo Wars.
 * In Halo: Reach, the HuCiv HC1500 tractor unit is an available drivable vehicle on some campaign levels. It is prone to oversteer similar to other civilian vehicles in the game, and it goes about half the speed of a Mongoose.
 * The only multiplayer map in Halo 3 to support it is Foundry.
 * Tractor units are not available in Halo: Reach's Forge mode on any maps, along with all civilian vehicles.
 * The Halo 4 multiplayer map Perdition has several tractor units, but the vehicles are unusable.

List of appearances

 * Halo 2
 * Halo: Ghosts of Onyx
 * Halo 3
 * Halo: Contact Harvest
 * Halo Wars
 * Halo: Blood Line
 * Halo: Reach
 * Halo 4
 * Halo 2: Anniversary