United Airlines will transfer baggage between aircraft with tugs and carts. Airlines
normally use these vehicles in transfer operations to back up mechanical systems in any
case, even at the most modern transfer midfield concourses, such as Pittsburgh and at
the United Airlines facility at Chicago/O'Hare. This kind of operation is relatively easy at
Denver because in an arrangement almost unique in the United States but standard at
busy airports in Europe and elsewhere there are separate roadways for apron
vehicles, located between the aircraft positions at the gates and the concourse building.
Using tugs for transfers is, however, a laborintensive, expensive operation.