D. Wylie Associates

The National Commercial Driver License (CDL): A Human Factors Success Story

A bus or heavy truck accident can cause far greater damage than an automobile accident. Therefore Congress required that federal standards be set for commercial drivers. Consequently, the US Department of Transportation (DOT) developed the Commercial Driver License (CDL) system now in use throughout the United States.

The US DOT and a committee of 13 states developed the CDL system by sponsoring a program to perform truck and bus skill and knowledge requirements analyses, identify classes of commercial motor vehicles that had differing skill and knowledge requirements, develop a Model CDL Driver’s Manual defining the minimum knowledge required to operate the various classes of vehicles, develop CDL knowledge (written) tests and skill (driving) tests, and conduct an operational evaluation of the system in several states. The evaluation was successful, the Commercial Driver License system was implemented by all the states, and over 9,000,000 CDL licenses have been issued so far under this system.

Dennis Wylie was a key human factors scientist on the CDL development team, leading the skill and knowledge requirements analyses. Fifteen skill/knowledge categories critical to safe truck and bus operation were identified. Each of the many bus, truck, and tractor trailer configurations in widespread use were evaluated with respect to each of the skill and knowledge categories, through extensive interviews with motor carriers, drivers selected for outstanding safety records, truck and bus manufacturers, truck and bus training schools, and commercial vehicle safety organizations. This work resulted in the present system of CDL license classifications and endorsements.

Dennis Wylie is also the principal author of the CDL Driver’s Manual, which defines the minimum knowledge requirements for operating the various classes of commercial vehicles, and is the basis for the questions in the CDL written tests. This 100-page manual is given by each state’s licensing agency to applicants preparing for the Commercial Driver License examinations. The manual includes sections on vehicle inspection, basic control, speed and space management, situation awareness, fatigue and alertness, mountain driving, air brakes, emergencies, cargo safety, and combination vehicles (tractor-semitrailer, double trailers, triple trailers, etc.).

After the US DOT and the committee of states approved the CDL licensing system, Wylie and his associates developed and conducted a “train-the-trainer” program for the lead CDL license examiners from each state licensing agency in the US. These examiners then trained additional license examiners and established CDL licensing programs in their respective states.

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