D. Wylie Associates
Human Factors Forensic Science in Collision Analysis


Human factors account for most traffic accidents. The tractor-trailer, truck, bus, or car driver has a duty to keep a proper lookout, and safe driving requires vigilance and sustained attention, timely hazard detection, reasonable decision making to choose a hazard avoidance strategy, and prompt control responses (steering, braking, etc.). Inattention and driver impairment underlie most crashes. Impairment of attention, hazard detection, decision making, and reaction time are often due to fatigue, drowsiness, lack of sleep, cumulative sleep debt, the body’s circadian rhythms, and the effects of alcohol and other drugs. Other significant causes of inattention include texting or talking on a cell phone and other distractions.

Dennis Wylie is an internationally recognized human factors expert concerning driver error; inattention and improper lookout; driver fatigue; car, truck and bus driver skill and knowledge requirements; driver and motor carrier standards of care; hours of service violations; circadian rhythms; sleep debt; impaired vigilance, alertness, decision making, reaction time, and control responses.

He directed the largest study of driver fatigue and alertness conducted in North America, a seven-year multimillion dollar international project that was the main factor in major revision of the Federal and state rules governing working hours for commercial truck, bus, and automobile drivers, including an increase in required off-duty time of 25%.

He and his colleagues also developed the national commercial driver licensing system. He is the principal author of the Commercial Driver’s Manual used by all state licensing agencies for licensing commercial truck, bus, and automobile drivers. The information in the Commercial Driver’s Manual defines the skill, knowledge and standard-of-care requirements for commercial drivers and is the basis of the commercial driver license (“CDL”) tests. He and his colleagues trained the first CDL Examiners of each state, who went on to train the others. All commercial drivers in the United States – more than 9,000,000 so far – have been licensed under the CDL system, which is set out in the Code of Federal Regulations at 49 CFR 383 “Commercial Driver’s License Standards.”

Dennis Wylie has published numerous peer-reviewed materials in his field, including the chapter titled “Commercial Motor Vehicle Collisions” in the Handbook of Human Factors in Litigation and the special editorial “Sleep, Science, and Policy Change” in the New England Journal of Medicine. He has been retained as a human factors expert in motor vehicle accidents by more than 200 attorneys (about 60% plaintiff, 40% defense) in 30 states.

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