In a recent game, a question arose about crewing. Two vehicles are in play, and one creature. Can you tap the one creature to crew both vehicles? I played it only being able to crew a single vehicle, and a quick look at the rules didn’t seem to clarify. What do you think?
-s
Fleetwheel Cruiser vehicle [wizards.com]
http://gatherer.wizards.com/Pages/Card/Details.aspx?multiverseid=417787

No. The “Crew” is a cost. So it must be paid for the vehicle to become a creature. You could tap the newly activated vehicle to crew another vehicle.
702.121 Crew
http://blogs.magicjudges.org/rules/cr702/#crew