This chapter defines the term "geometric design" as the three-dimensional features of a highway that relate, affect, or are directly related to its operational quality and safety. These features, visible to the driver, include the cross section (lanes and shoulders, roadside slopes, and clear areas), intersections, channelization, interchanges, and the horizontal and vertical alignment of the highway. Geometric design translates operational experience and research into the actual highway. It thus reflects the human characteristics of drivers, as well as the physical and operational characteristics of vehicles. Geometric design also involves a knowledge of construction and maintenance costs and other considerations. For many reasons, geometric design is and will always be dynamic. The age and abilities of the driving population as well as their desires and expectations are changing over time. So, too, are the vehicles on the highways. Societal values also change over time, with resulting effects on what is considered reasonable or good geometric design. Environmental concerns, energy conservation, and other issues have influenced geometric design.
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