A clicker...learn to use a clicker...and mark even so much as a step closer to the vehicles. I wouldn't just let her stand there and freeze up either. I would get her "crack" out...whether it's toys or food...and keep her moving. Walk away, keep her focused and then walk back towards it. Don't let her get to the point where she is reacting. Turn back away right before you reach her threshhold.
Look up BAT.
~The strength of one's opinion should not exceed their knowledge on the matter~