three or more lanes in each direction, both shoulders are to be at least wide. In mountainous terrain, a left shoulder of and a right shoulder of are acceptable, except where there are at least four lanes in each direction, in which case both shoulders are to be at least wide. In places with higher truck traffic, over 250 Directional Design Hour Volume, wider shoulders should be considered. Pavement sloping: On straight sections of the highway, the roadway is to have a cross slope of at least 1.5%, and preferably 2% to ensure proper drainage, with up to 2.5% in areas of heavy rainfall. The cross slope of both the left and right shoulders should be between 2% and 6%, but not less than the main lanes. Median width: The median should have a width of least , and preferably , in rural areas, and , plus a barrier, in urban or mountainous areas. Recovery areas: There should be no fixed objects in the clear zone, the width of which should be determined by the design speed in accordance with the current edition of AASHTO's Roadside Design Guide. When this is not possible, breakaway supports or barriers guarding the objects should be used. Special care should be taken in depressed highways, where piers and walls should be placed at least beyond the outer edge of either shoulder. Slopes in the clear zone should be at most 1:4, and should typically be 1:6. Curbs: No curb is to be placed nearer to the roadway than the outside edge of the paved shoulder. Any curb is to have a sloping, and not a vertical, face and be no more than in height. Special care should be taken when curbs are combined with barriers. Vertical clearance: The minimum vertical clearance under overhead structures, such as bridges, is , including both paved shoulders and an allowance for extra layers of pavement. Through urban areas, at least one routing is to have clearances, but others may have a lesser clearance of . Sign supports and pedestrian overpasses must be at least above the road, except on urban routes with lesser clearance, where they should be at least higher than other objects. The cross bracing of truss bridges has a special additional clearance requirement of . Bridges: Bridges less than long should carry the full width of the roadway, including the paved shoulders. Longer bridges can