M274 Mongoose

The Marines' fastest ground vehicle is the Mongoose All-Terrain Vehicle. Essentially four wheels and an engine, this ATV can travel very fast over nearly all types of terrain. With no weapons on board, the driver must use his own weapons for defense, though this means taking one hand away from the vehicle's already precarious controls. Due to this, the driver would use a weapon with the ability of Dual Wielding if he could use it with one hand (It is to be seen if this ability is possible in Halo 3, most likely the passenger would be able to fire instead). It serves a similar purpose of the Covenant Ghost. There also is a passenger seat on the rear, behind the driver. This is called "Riding Brokeback," from the option in the Halo 3 preview - "Press RB to ride Brokeback." The message flashed on the screen as Bungie demoed the four-wheeler.

This vehicle did not make it into the final version of Halo 2 due to the fact of the Mongoose not being able to behave as well as Bungie wanted, but is going to be in Halo 3 for granted.