In Speed why does Payne take Annie hostage?
He saw the recording had been looped, and so he knew Jack and the others were probably off the bus at that point, or that the police were working on a plan of some kind. He can even see the police in the windows across the street. He must've known that, even though he saw them drop the money in the garbage can, it was probably rigged with a tracker, the paint bomb, or something. He knew they weren't just going to give him all that money.
So why bother to take Annie as a hostage at all?
If he's that hellbent on getting the cash, even with the possibility of a tracking device, why not just slip down into the subway (at this point, the police don't know about the hole in the sidewalk) and run off with the money?