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 PRINCIPLES OF LANDSCAPE DESIGN

Highway design, in the broadest sense, rests upon landscape principles as well as upcn the more commonly recognized engineering principles of alinement, profile, grade cross-section, roadway and right-of-way width, drainage, and structural strength and durability. A balanced agreement with the two sets of principles characterizes the best design.

Flowing rather than abrupt change of gradient and alinement are necessary from the engineering standpoint for promotion of the safety and ease of vehicular movement and for increase in the highway’s traffic discharge capacity. They are equally necessary to fit the road gracefully into its natural environment, which is the essence of good landscaping.

Flattened slopes of excavation and embankment and a well-rounded cross-sectional contour are essential to prevent soil erosion and to minimize the risks of injury and damage when vehicles accidently or unavoidably leave the roadway. They are needful also to mold the highway into the terrain and to make it a harmonious feature of the natural landscape.

Marginal land strips, publicly owned or controlled, are required for the engineering reason of protection of vehicles moving on the highway against collision with entering vehicles, and of operators of moving vehicles against various roadside distractions. For landscaping reasons marginal land strips are needed to make possible a pleasing transition between the lines and plantings of the highway and the natural slopes and growth of the adjacent lands, to permit the screening of unsightliness, and to provide stopping space from which to view unfolded natural beauty.

If engineering principles require a certain monotony of smoothness and attention-lulling security in the roadway design, the appropriate application of landscaping principles can relieve the monotony and promote the safety of traffic by reawakening the interest and attention of drivers.

The interregional highways, in their rural sections especially, will serve a traffic composed in large degree of vehicles driven in the pursuit of pleasure or recreation. Sound landscape design will increase the pleasure and relieve the strain of all journeys.

In their urban and suburban sections, the interregional routes will carry a heavy, bustling traffic. Adequately landscaped borders will eliminate the traffic hazards of closely crowding buildings, and insulate adjacent residential and business properties, churches, and schools from the noise, dust, and fumes of traffic.

Landscaping for rural sections of the system.—Consideration of landscaping desiderata should pervade all stages of the location, design, and construction of rural sections of the interregional system, and a proper regard for landscape principles in the design will simplify and 89