You are good at combining cars and guns, or planes and guns, horses and guns, whatever, as long as it moves. Normally, it is a continuos action to shoot or dodge (or whatever) while in a moving vehicle or driving, but you ignore this penalty. You can still shoot normally, even while clinging to the outside of a speeding car. You also ignore the Move of your target when figuring how difficult it is to hit, as well as any modifiers for bumpy rides, high winds, and similar hazards.