When BatMan commands his Batmobile to stop after it comes to him all by itself, you see him talking into his little remote control thingy. The next time you see him, it is not next to his face. Immediatly following that scene, you see the remote control thing back up to his face again. Quick arms, huh?
The real reason is this blooper, is that it is not Michael Keaton. It is a dummy or waxwork version of the actor. He wouldn't risk a limb standing in front of speeding (and braking) bat mobile. If you look carefully again, he is so stiff (scared stiff, anyone?)
The scene wherein Batman tells the Batmobile to stop and it stops within inches of him was almost certainly filmed forward and played in reverse. They wouldn't bother with waxworks just to film this scene when it's so easy to do it the other way.
Firstly it is him and it probably was filmed in seperate takes (I.E. one of the batmobile and batman and a seperate one of vale doing her small scream jump two differant seperate shots melded together) but the communicator thing was by his face the whole time. i just saw it like ten times.