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162 of air and light. For an appropriate distance inward from the portal the intensity of artificial light provided during the day shall be sufficient to afford such a transition between outer daylight and the normal tunnel lighting as will permit safe entrance into the tunnel without reduction of the speed of vehicles.

''VI. Pedestrian facilities.''

On rural sections of the system pedestrian use of road surfaces and pavements and shoulders shall be prohibited. Adequate pedestrian paths shall be provided whenever the need justifies.

Wherever other public highways are carried over or under a rural section of the interregional system, provision shall be made for safe pedestrian crossing of the interregional highway, if necessary, by means of adequate walks outside the vehicular curbs of underpassing highways or overpassing bridges. At other points where need is found to exist, special pedestrian underpasses or overpasses with connecting walkways shall be provided.

''VII. Landscaping.''

On all rural sections of the system the design, wherever feasible, shall conserve desirable and irreplaceable landscape features, avoid needless damage to desirable trees and other growth and to lake and stream shores, and preserve natural sites for the development of overlooks, picnic areas, and other desirable wayside attractions. Unnecessary construction scars shall be avoided. Borrow pits shall not be permitted within sight of the road unless they are adjusted and recovered to avoid unsightliness. All ground surfaces disturbed by construction shall be appropriately recovered with suitable vegetative growth, and additional landscaping shall be done where deemed necessary.

The design, combined with re-covering of disturbed surfaces and other landscaping, shall be planned to protect the highway against erosion by wind and water, to reduce maintenance to a minimum, and to enhance the natural appearance of the road and the wayside.

''VIII. Signs and pavement markings.''

The design of rural sections of the interregional system shall be such as to reduce to a practicable minimum the necessity of cautionary signs and pavement markings. The installation of traffic control signals shall be prohibited.

The form, dimensions, color, and style and size of all lettering of all signs, the legend of all cautionary signs, and the form, dimensions, character, and significance of all pavement markings shall be uniform throughout all rural sections of the interregional system in all States.

Route markers.—It is recommended that all interregional highways be incorporated in the United States system of numbered highways, and that all rural sections of the system be marked with standard U S route markers appropriately illuminated or reflectorized for night visibility. If two or more U S numbered routes incorporate the same section of any interregional highway, standard U S route