Vertical clearance. Minimum vertical
clearance under overhead structures (including over the paved shoulders) of 16 ft (4.9 m) in rural areas and 14 ft (4.3 m) in
urban areas, with allowance for extra layers of
pavement. Through urban areas at least one routing should have 16 ft (4.9 m) clearances. Sign supports and pedestrian overpasses must be at least 17 ft (5.1 m) above the road, except on urban routes with lesser clearance, where they should be at least 1 ft (0.3 m) higher than other objects. Vertical clearance on through
truss bridges is to be at least 17 ft (5.1 m).