Recognizing that professional drivers need specialized skills to operate large commercial vehicles and the often sensitive loads they carry, the United States Congress has mandated uniform national standards for knowledge and skills testing through the Commercial Driver License Law (CDL).... This manual has been designed to help truck and bus drivers prepare for both the knowledge and behind the wheel tests for commercial licenses. Consistent with the intent of the CDL program, it is also intended, in a practical way, to assist commercial drivers with acquiring and refining the tools necessary to assure their safety and the safety of all highway users. -A message for commercial drivers.