JJ Keller Entry Level Driver Training for CDL (Commercial Driver’s License) Practice Test

The coupling system is essential for connecting the tractor to the trailer. This system includes components such as the fifth wheel assembly and the kingpin, which allow the tractor to securely attach to the trailer. Proper coupling ensures stability and control during transport, preventing separation or swaying while on the road. The coupling system is engineered to handle the significant forces exerted while driving and helps maintain the alignment of the tractor and trailer.

Other systems, such as the suspension system, support the weight and enhance ride quality, but they do not connect the trailer to the tractor. The drivetrain is responsible for transmitting power from the engine to the wheels, while the hydraulic system manages braking and other functions but does not play a role in connecting the two vehicles. Thus, the coupling system is the correct answer, as it specifically facilitates the crucial connection between the tractor and trailer.