Have you guys seen the Halo 2 bonus DVD? It has a whole bunch of vehicles that were supposed to be in Halo 2, but they took them out because there wasn't enough time to incorporate them into the gameplay. Well, maybe Bungie will bring those vehicles (like the ATV) into Halo 3.
The only thing that confuses me is this: why would humans, in 500 years in the future, still be driving in vehicles that use fuel and run on wheels? Looking at how much technology has progressed in 100 years of real time, you would think that people would make radically advanced new ways of transportation and warefare... hmmm....