opposite banks of a stream or on the two sides of a local depression or rock outcropping, will likewise reduce costs and at the same time permit the conservation of interesting features of the natural landscape. And, even where there is no topographic reason for doing so, an opportune slight variation of the curvature of the two roadways will alter the width of the median strip and relieve the monotony of long parallel lines, without effect upon the total requirement of right-of-way width. An important result of all such variations in the lines and grades of the two roadways will be realized in reduction of the hazards of headlight glare in night driving.
As in the location and construction of the routes, design for utility and economy is found to go hand in hand with sound landscape design, so also a properly landscaped highway will be a highway easy to maintain. The flattened side slopes will favor the growth of vegetation, prevent erosion and thus remove the cause of much troublesome clogging of the drainage system. The easier slopes can be mowed by machine instead of by hand methods, and the streamlined contours of cut banks will reduce snow drifting and facilitate machine methods of snow removal.
It will be observed that there has been no mention in the foregoing of the tree planting that is so widely associated with the idea of roadside improvement. The omission has been intentional. There is no place in sound rural highway landscaping for the regular or row planting of trees. The objective should be the preservation or, where necessary, the re-creation of a natural foreground environment in harmony with the distant view. To that end, existing well-placed and beautiful trees should be preserved wherever possible; unpleasing and view-obstructing growth should be removed; and only where the irregular introduction of trees and other growth will serve to highlight the natural beauty of the roadside view or where it is especially desirable to screen unsightly or distracting objects or activity should the replanting of trees receive consideration. Trees replanted for such reasons should be invariably native to the environment.
The landscaping of urban sections.—In cities and their nearer suburban areas the opportunity for employment of the locational devices of landscape treatment will be more limited. But the general straightness of right-of-way alinement there necessary for avoidance of conflict with the existing street plan need not confine the roadways of the interregional routes to rigidly straight lines. Within a block-wide right-of-way the separate roadways may be constructed at different levels in adaptation to an existing transverse slope. The grades of both roadways may be gracefully rolled, dipping to pass under bridges at the crossing streets and rising between to approximate the level of the existing streets which form the local service ways. As they rise and fall the separate roadways may be caused to diverge and converge in alinement, thus varying the width of the median strip. Or the two roadways may be swung to one side of the right-of-way with only a narrow median strip intervening there, for example, to pass under a crossing bridge located off-center with respect to the right-of-way. To gain space for desirable widenings of the median strip or lateral park areas, retaining walls may be used to reduce the width required for slopes in depressed sections, but these should preferably be constructed at the edge of the service ways and never in cramping proximity to the roadways of the express route. The widened central or lateral areas may be used for appropriate plantings or for rest or playground area
