page_title: Interstate Highway standards
section_title: Standards
hierarchical_section_title: Interstate Highway standards / Standards
caption_attribution_description: English: Interstate Highway Under Construction
context_page_description: Standards for Interstate Highways in the United States are defined by the American Association of State Highway and Transportation Officials in the publication A Policy on Design Standards: Interstate System. For a certain highway to be considered an Interstate Highway, it must meet these construction requirements or obtain a waiver from the Federal Highway Administration.
context_section_description: These standards are, as of May 2016:
  Controlled access: All access onto and off the highway is to be controlled with interchanges and grade separations, including all railroad crossings. Interchanges are to provide access to and from both directions of the highway and both directions of the crossroad. Interchanges should be spaced at least 1 mi (1.6 km) apart in urban areas and 3 mi (4.8 km) apart in rural areas; collector/distributor roads or other roadway configurations that reduce weaving can be used in urban areas to shorten this distance.
  In urban areas, there should be no driveways or other access points to adjacent properties along the crossroad for at least 100 feet (30 m) from entrance and exit ramps, in both directions, and for at least 300 feet (91 m) in rural areas.
  In urban and suburban areas, consideration should be given to accommodating bicycles and pedestrians along crossroads.
  Minimum design speed: A minimum design speed of 70 mph (113 km/h) is to be used, except in mountainous and urban areas, where the minimum is 50 mph (80 km/h).
  The sight distance, curvature and superelevation of the highway should follow the current edition of AASHTO's A Policy on Geometric Design of Highways and Streets for the chosen design speed.
  Maximum grade: The maximum permissible vertical angle, or grade, along the highway is determined from terrain and design speed, with up to 6% generally allowed in mountainous areas, 5% in rolling terrain, and 4% on level terrain. An additional 1% is allowed in urban areas.
  Minimum number of lanes: There are to be at least two lanes in each direction, unless more are necessary for an acceptable level of service, according to the current edition of AASHTO's A Policy on Geometric Design of Highways and Streets. Climbing lanes and emergency escape ramps should be provided where appropriate.
  Minimum lane width: The minimum lane width is 12 feet (3.7 m), identical to most US and state highways.
  Shoulder width: The minimum width of the left paved shoulder is 4 feet (1.2 m), and of the right paved shoulder 10 feet (3.0 m). With three or more lanes in each direction, both shoulders are to be at least 10 feet (3.0 m) wide. In mountainous terrain, a left shoulder of 4 feet (1.2 m) and a right shoulder of 8 feet (2.4 m) are acceptable, except where there are at least four lanes in each direction, in which case the both shoulders are to be at least 8 feet (2.4 m) 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 50 feet (15 m), and preferably 60 feet (18 m), in rural areas, and 10 feet (3.0 m), 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 2 feet (0.61 m) 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 4 inches (10 cm) 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 16 feet (4.9 m), including both paved shoulders and an allowance for extra layers of pavement. Through urban areas, at least one routing is to hav
caption: An Interstate Highway under construction, with both directions of traffic moved to one side of the roadway
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