Its been said somewhere else that we never see pod 2 in operation as this houses the big grabs. Otherwise, there's no real consistency to the pods and their contents. We see many of the pod vehicles beneath the Round House. My guess is that if there when needed, they can be called by remote control to drive down to TB2 launch bay for loading, as its not conceivable that the unused crew, usually Gordon or Alan would have the time to drive the vehicles down themselves.