§ 383.110 states the requirement in one line: all drivers of commercial motor vehicles must have the knowledge and skills necessary to operate one safely, and the subpart sets what a State must include in the tests it gives applicants. § 383.111(a) then makes that concrete with twenty general areas of required knowledge — not twenty questions, but twenty subjects any State’s knowledge test must reach.

They fall into recognisable families. Four are about the rules and the machine: safe operations regulations, safe vehicle control systems, commercial motor vehicle safety control systems, and vehicle inspections. Six are about handling the vehicle itself: basic control, shifting, backing, speed management, space management, and the relationship of cargo to vehicle control. Five are about reading and reacting to the world outside: visual search, communication, hazard perceptions, emergency maneuvers, and skid control and recovery. And five are about conditions that change everything: night operation, extreme driving conditions, mountain driving, hazardous materials, and fatigue and awareness. Grouping them that way is a study aid rather than a structure the rule imposes — § 383.111 lists them flat — but the families are how the material actually behaves.

One of the twenty deserves separate notice because of how far it reaches. The first area, safe operations regulations, is defined as the driver-related elements of the regulations contained in parts 391, 392, 393, 395, 396 and 397 of the subchapter. That is qualification, driving rules, equipment, hours of service, inspection and maintenance, and hazardous materials routing — six other Parts, folded into one item on a twenty-item list. The knowledge test is deliberately broader than Part 383, which is why nearly every later chapter of this book is also test material.