Which vehicle is primarily used for the transportation of passengers' luggage?

The baggage cart tractor is specifically designed for the efficient transportation of passengers' luggage at airports. This vehicle plays a crucial role in ground handling operations, allowing the movement of large numbers of baggage carts containing passenger luggage between the terminal building and aircraft. Typically, it is equipped to pull multiple baggage carts at once, optimizing the flow of luggage from check-in to the aircraft, as well as during the unloading process upon arrival.

The other options serve different purposes that do not primarily focus on passenger luggage transportation. For instance, the ground power unit delivers electrical power to aircraft when they are on the ground, while the air start unit is used to provide engine start assistance to airplanes. The lower deck loader is utilized for loading and unloading cargo and baggage into the aircraft’s cargo hold but is not specifically a vehicle for transporting luggage over distances in the airport setting. Thus, the proper identification of the baggage cart tractor highlights its dedicated function in the logistics of airport operations concerning passenger luggage.