You've probably seen out on the road a chain of Heavy trucks stacked up on each other. This is a way to transport 2-4 trucks at a time, and save on fuel and time. You need a heavy duty wrecker with a minimum of 20,000 lbs carrying capacity to load and unload the trucks.
The wrecker must accommodate itself to where the truck being unloaded. Once the wrecker is in place, it has to secure the loaded truck. the loaded truck has to have the saddle bolts loosened. Once everything is secured, the wrecker lifts the truck in midair, and the power unit moves forward. The wrecker then proceeds to lower the boom until the loaded truck is secured on the ground. Its a heart pounding procedure, luckily the people in charge are professionals.