I have a hard enough time with the scant 1/4" seam and matching points just sewing at my desk, I dont think i would be happy with the results of sewing while on a sometimes bumpy ride. LOL
My concern would be riding down the highway with a sewing machine in your lap, what happens if God forbid you're in an accident and the airbags go off? The force of the airbag hitting the machine and slamming it into you could really do some damage to you, or the machine could go airborne and hurt the driver or a backseat passenger.