Details like the donor vehicle, top speed and source of the Graf/Hauptman Solar/Saline Actuator are "classified." But we do know that it's being built to scale, which means it is sized for Master Chief Petty Officer John-117, more commonly known as Master Chief, who happens to be seven feet tall when he's all geared up.
So you probably won't be able to reach the pedals, but no matter, everybody wins with this. Except the Flood. Or whoever ends up challenging the UNSC in Halo 4. Check out the G4TV video segment below.