The elements of design must be thoroughly investigated by the 
planning and design engineer. User requirements are determined 
by the planned development of an area, the traffic between various 
points within the area, through traffic, and the specific requirements 
of the road user along the route. These are well defined in the 
Bureau of Public Roads planning procedures for metropolitan areas, 
and are adaptable to rural areas. 
Determining precise road location is the most difficult job that 
can be assigned a highway engineer. Not all objectives are com- 
patible. Total cost must be a strong factor. Various watershed 
problems such as erosion, pollution, change of ground water table, 
and local flooding must be either avoided or controlled. Other 
considerations include: (1) How well the road serves the abutting 
lands; (2) whether the highway provides reasonabie access; (3) 
whether the area’s resources development is enhanced rather than 
disrupted; and (4) economic aspects from the standpoint of the 
lowest operating costs to the user. The cost of maintaining the road 
structure and its appurtenances must be reasonable. Design ele- 
ments of safety and esthetics, though difficult to evaluate on an 
economic basis, must also be seriously considered. 
Many tools are available to assist in the solution of these problems. 
One of these is the topographic map, but others are equally impor- 
tant. Planning commission development plans and zoning maps 
should be used. For many areas, soil-type maps are published by 
the Soil Conservation Service of the U.S. Department of Agricul- 
ture. These maps are invaluable in locating suitable areas for 
roadbuilding and potential problem areas. They are also excellent 
guides to the type of developments which may eventually occur in 
an area. Other planned developments, such as reservoirs and flood 
control works which will be major attractions to the road user, must 
be considered in the initial road-planning stages. 
In addition to published materials, many experts in fields such as 
44 
fish and wildlife, water development, and landscape architecture 
are available to the highway engineer for information on the environ- 
ment in which he is building. 
Watershed protection has been mentioned as a requirement in the 
location and design of roads. The natural characteristics of streams 
must not be interrupted adversely. Channel changes in firmly en- 
trenched streams should be minimized, and encroachment on stream 
channels must be avoided or adequately protected. Additional 
measures, such as careful routing to prevent earth movement and 
balancing of cut and fill, should be taken whenever practical. Sys- 
tems for the collection and discharge of surface water must be 
designed with due regard for the protection of embankments and 
fills and the erosive effect of additional water on minor channels. 
All disturbed areas subject to erosion must be revegetated or other- 
wise protected. 
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The designer must consider basic relations between road design and the 
terrain. Long straight tangents and short-radius curves should be avoided. 
In any terrain condition they appear foreign to the environment. The 
designer must break with the traditional concept of straight lines between 
location controls, connected by circular curves. Using flowing curves with 
short tangents or spirals can fit the road into the landscape. 
