“Human factors is the scientific discipline that studies how people interact with devices, products, and systems. It is an applied field where behavioral science, engineering, and other disciplines come together to develop the principles that help assure that devices and systems are usable by the people who are meant to use them. The field approaches design with the “user” as its focal point. Human factors practitioners bring expert knowledge concerning the characteristics of human beings that are important for the design of devices and systems of many kinds. The discipline contributes to endeavors as complex as space exploration and to products as simple as a toothbrush. In the field of transportation engineering, there have been numerous important contributions from human factors, but these are not always self-evident. Sight distance requirements, workzone layouts, sign placement and spacing criteria, dimensions for road markings, color specifications, sign letter fonts and icons, signal timing – these and many more standards and practices have been shaped by human factors evaluation. As applied to highway safety, human factors is concerned with the design of the roadway and operating environment and the vehicle. The three primary components of the highway transportation system – the roadway, the vehicle, and the road user – all must be compatible with one another. Engineers can design roadways, traffic control devices, and vehicles, but they cannot design the road user. They can design for the road user. Human factors provides an objective basis for doing this. It is based on measured behavior and capabilities rather than assumptions or trial-and-error.”

Lerner, N.; Llaneras, R.; Smiley, A.; Hanscom, F. Comprehensive Human Factors Guidelines for Road Systems. National Cooperative Highway Research Program. Transportation Research Board of the National Academies. March 2005. Page B-4.