When speaking about the gross weight of any vehicle, it is the total weight of the vehicle and its payload that is being referred to. The weight of the payload can be easily identified by subtracting the vehicle's weight from the gross weight of the loaded vehicle. It is important to note that a vehicle's gross weight is referring to the vehicle full of fluids and with a full amount of passengers on board as well. When examining road weight restrictions, it is the gross weight of the loaded vehicle that must fall under the load limit restriction.
In airplane flight, a given air frame and engine combination is only rated to carry a certain gross weight. The pilot must take the calculation of the fueled plane's weight plus the weight of all passengers and subtract that figure from the gross weight rating of the plane to know how much cargo can be loaded safely. Failure to accurately do the math can result in a plane that will not leave the ground or one that will not remain in flight or gain proper altitude once airborne. Often the weather must be figured into this variable calculation as well in order to accurately factor the flight load limit.
In rail transport, the figure becomes critical when crossing bridges. Many bridges have seasonal load restrictions much like highways. Only a train with correct load spacing may cross the bridge at a given time. It becomes extremely critical for the team lining up the rail cars to place certain cars together while spacing some cars out in order to have only a predetermined weight of cars on the bridge span at one time. In some parts of the world, many trains also have weight restrictions on them yearlong depending on the climate and the type of soil the track is laid on.
Understanding gross weight is a valuable tool for many different scenarios in the transportation business. Mechanics designing braking systems and draw bar hitches must also understand gross weight in order to correctly design the proper system for the intended vehicle. Installing a brake shoe designed for a light-weight vehicle onto a heavy vehicle will result in prematurely worn or damaged brakes. This is the same information that must be used and understood when purchasing tires for a vehicle; not purchasing the correct tires will result in a failed tire or damaged equipment.