1、1 A Policy on Design StandardsInterstate System A Policy on Design Standards Interstate System May 2016 2016 by the American Association of State Highway and Transportation Officials. All rights reserved. Duplication is a violation of applicable law. Cover photo courtesy of Florida Department of Tra
2、nsportation. Photo depicts the I-10/I-95 Interchange “The Big I” Project. The project was the Grand Prize winner for AASHTOs 2011 Americas Transportation Award Competition. 2016 by the American Association of State Highway and Transportation Officials. All rights reserved. Duplication is a violation
3、 of applicable law.ii A Policy on Design StandardsInterstate System EXECUTIVE COMMITTEE 20152016 OFFICERS: PRESIDENT: Paul Trombino, Iowa VICE PRESIDENT: David Bernhardt, Maine SECRETARY-TREASURER: Carlos Braceras, Utah EXECUTIVE DIRECTOR: Bud Wright, Washington, DC REGIONAL REPRESENTATIVES: REGION
4、I: Leslie Richards, PennsylvaniaPete Rahn, Maryland REGION II: Paul Mattox, West VirginiaCharles Kilpatrick, Virginia REGION III: Charles A. Zelle, MinnesotaRandall S. Blankenhorn, Illinois REGION IV: Brian Ness, IdahoCarlos Braceras, UtahIMMEDIATE PAST PRESIDENT: Vacant 2016 by the American Associa
5、tion of State Highway and Transportation Officials. All rights reserved. Duplication is a violation of applicable law.iii A Policy on Design StandardsInterstate System TECHNICAL COMMITTEE ON GEOMETRIC DESIGN 20152016 Jeff Jones, Tennessee, Chair James Rosenow, Minnesota, Vice Chair Elizabeth Hilton,
6、 Federal Highway Administration, Secretary Patricia Bush, AASHTO Liaison Voting Members Mike Fugett, Arkansas Kevin Herritt, California Brent Story, Georgia Deanna Maifield, Iowa Jim Brewer, Kansas Eric Marabello, Maryland Stanley Wood, Massachusetts Richard Wilder, New York Chad Frisinger, North Da
7、kota Kent Belleque, Oregon Mark Leiferman, South Dakota Barton Thrasher, Virginia Non-Voting Members Joe Ruffer, National Association of County Engineers Robert Wunderlich, National League of Cities Reza Maleki, Port Authority of New York and New Jersey Marshall Elizer, American Public Works Associa
8、tion 2016 by the American Association of State Highway and Transportation Officials. All rights reserved. Duplication is a violation of applicable law.iv A Policy on Design StandardsInterstate System TABLE OF CONTENTS General 1 Design Traffic . 1 Right of Way 2Right of Way 2Access Control . 2 Geomet
9、ric Controls and Criteria 3Design Speed . 3Sight Distance 3Curvature and Superelevation . 3Gradients 3 Cross Section Elements 4Number of Lanes . 4Width o f T r affic Lanes 4Shoulders 4Traveled Way and Shoulder Cross Slope . 5Medians . 5Roadside Design . 5Sideslopes 5Curbs 6Multimodal Accommodations
10、6 Interchanges 6 Bridges and Other Structures . 7General 7Vertical Clearance . 7Cross Section . 7Design Loading Structural Capacity . 8Existing Bridges to Remain in Place . 8Tunnels 8 2016 by the American Association of State Highway and Transportation Officials. All rights reserved. Duplication is
11、a violation of applicable law.1 A Policy on Design StandardsInterstate System GENERAL The Dwight D. Eisenhower National System of Interstate and Defense Highways (Interstate) is the most important highway system in the United States. It carries more traffic per mile (kilometer) than any oth- er comp
12、arable national system and includes the roads of greatest significance to the economic welfare and defense of the nation. The highways of this system are to be designed in keeping with their impor- tance as the backbone of the nations highway systems. To this end, they are designed to provide safety
13、 and mobility for predicted growth in traffic. These objectives can be realized by conscientious attention to design. The following minimum stan- dards apply to Interstate highway segments constructed on new right-of-way and segments undergo- ing reconstruction along existing right-of-way. The geome
14、tric design standards used for resurfacing, restoration, and rehabilitation (3R) projects may be the AASHTO Interstate standards that were in effect at the time of original construction or inclusion into the Interstate system. Design values are presented in this document in both U.S. customary and m
15、etric units and were devel- oped independently within each system of units. The relationship is neither exact (soft) nor a com- pletely rationalized (hard) conversion. The values are those that would have been presented in either system. Therefore, the user is advised to work entirely in one system
16、and not attempt to convert direct- ly between the two. In addition, all projects, including 3R, or elements of projects that retain existing geometrics meeting the minimum standards for the selected design speed in one system of units are considered in compliance with comparable design speed standar
17、ds in the other. The current editions of AASHTOs A Policy on Geometric Design of Highways and Streets (“The Green Book”) and the AASHTO LRFD Bridge Design Specifications shall be used as design guides where they do not conflict with these standards. DESIGN TRAFFIC The Interstate highway system is de
18、signed to safely and efficiently accommodate the volumes of passenger vehicles, buses, trucksincluding tractor-trailer and semi-trailer combinations, and corre- sponding military equipmentestimated for the design year. The design year for new construction and reconstruction should be at least 20 yea
19、rs beyond the year in which the plans, specifications, and estimate for construction of the section are approved. The traffic volumes used for design should be the appropriate hourly volume of the design year, usually referred to as the design hourly volume (DHV) in vehicles per hour (vph). The DHV
20、is the total traffic in both directions of travel. The directional design hourly volume (DDHV) (vph) is the directional distribu- tion of traffic on multi-lane facilities during the design hour. Refer to AASHTOs Green Book for discus- sion on designing for future operating conditions. 2016 by the Am
21、erican Association of State Highway and Transportation Officials. All rights reserved. Duplication is a violation of applicable law.2 A Policy on Design StandardsInterstate System RIGHT-OF-WAY Right-of-Way The width of right-of-way shall be sufficient to accommodate the roadway cross section element
22、s and requisite appurtenances necessary for an adequate facility in the design year. Acquisition of right-of- way sufficient to accommodate anticipated future improvements should be considered. Access Control Access to the Interstate system, including ramps, shall be fully controlled. The Interstate
23、 highway shall be grade separated at all railroad crossings and selected public crossroads. At-grade intersections shall not be allowed. To accomplish this, all intersecting roads are to be grade separated, terminated, rerout- ed, and/or intercepted by frontage roads. Access is to be achieved by int
24、erchanges at selected public roads. Access control shall extend the full length of ramps and ramp terminals at the crossroad or frontage road. Such control shall either be acquired outright prior to construction or by the construction of front- age roads or by a combination of both. Controlling acce
25、ss on crossroads in the vicinity of interchanges can provide significant benefits to traffic operations and safety performance through the interchange area. Access control beyond the ramp terminals should be achieved by purchasing access rights, provid- ing frontage roads, or prohibiting driveways.
26、Determination of the access control limits should be based on an evaluation that considers variables such as the: Functional classification of the crossroad; Volume of through movements, turning movements, and weaving maneuvers; Type of access (right turn only, left turn from crossroad, left turn fr
27、om access, or intersection); Number of lanes; Design of medians and turn lanes; and Observed and predicted safety and operational performance. A break in access control on the crossroad or frontage road should be no closer to the ramp terminal than 100 ft (30 m) in urban areas and 300 ft (90 m) in r
28、ural areas. Extended areas of access control may be needed to provide adequate safety and operation of the intersection(s). Refer to AASHTOs Green Book and the Transportation Research Boards Access Management Manual for additional details and guidance for access spacing in interchange areas. 2016 by
29、 the American Association of State Highway and Transportation Officials. All rights reserved. Duplication is a violation of applicable law.3 A Policy on Design StandardsInterstate System GEOMETRIC CONTROLS AND CRITERIA Design Speed Design speeds on the Interstate system shall meet or exceed the foll
30、owing values: Table 1. Design Speed Context Minimum Design Speed (mph) Minimum Design Speed (km/h) Rural (non-mountainous) 70 110 Rural (mountainous) 50 80 Urban 50 80 Sight Distance The minimum stopping sight distance shall be established in accordance with the procedures contained in the current e
31、dition of AASHTOs Green Book. Curvature and Superelevation Curvature and superelevation shall be designed in accordance with the current edition of AASHTOs Green Book. Gradients Maximum grades as a function of the design speed and the type of terrain shall be in accordance with the following table:
32、Table 2. Maximum Grades Type of Terrain U.S. Customary Metric Design Speed (mph) Design Speed (km/h) 50 55 60 65 70 75 80 80 90 100 110 120 130 Grades (%)* Grades (%)* Level 4 4 3 3 3 3 3 4 4 3 3 3 3 Rolling 5 5 4 4 4 4 4 5 5 4 4 4 4 Moun- tainous 6 6 6 5 5 6 6 6 5 * Grades 1% steeper than the value
33、 shown may be used in urban areas. 2016 by the American Association of State Highway and Transportation Officials. All rights reserved. Duplication is a violation of applicable law.4 A Policy on Design StandardsInterstate System CROSS SECTION ELEMENTS Number of Lanes Interstate highways shall have a
34、 minimum of two through-traffic lanes for each direction of travel. For new location projects, the number of lanes provided shall be sufficient to demonstrate an acceptable operational condition associated with the anticipated DHV in the design year. Projects in existing corri- dors shall provide en
35、ough lanes to demonstrate that the facility will operate as well or better than the no-build condition in the design year. Refer to AASHTOs Green Book for guidance in designing for future operating conditions. On ascending grades that exceed the critical design length, a climbing lane analysis shoul
36、d be per- formed and climbing lanes added where appropriate. Likewise, on extended lengths of maximum or near maximum descending grades, emergency escape ramps should be added where an analysis indi- cates they are appropriate. Width of Traffic Lanes All traffic lanes shall be at least 12 ft (3.6 m)
37、 wide. Shoulders Minimum paved shoulder widths in each direction of travel as a function of terrain and the number of through lanes shall be in accordance with the following table: Table 3. Minimum Paved Shoulder Widths One-Direction- al No. Through lanes Terrain Left Shoulder (ft) Right Shoulder (f
38、t) Left Shoulder (m) Right Shoulder (m) 2-lane Level or Rolling 4 10 1.2 3.0 3-lane or more Level or Rolling 10 10 3.0 3.0 2 or 3-lane Mountainous 4 8 1.2 2.4 4-lane or more Mountainous 8 8 2.4 2.4 Where truck traffic exceeds 250 DDHV, additional shoulder width may be beneficial. Refer to AASHTOs Gr
39、een Book for more information. Additional guidance on shoulder widths for tunnels and long bridges overall length over 200 ft (60 m) is provided later in this document. 2016 by the American Association of State Highway and Transportation Officials. All rights reserved. Duplication is a violation of
40、applicable law.5 A Policy on Design StandardsInterstate System Traveled Way and Shoulder Cross Slope On tangent sections, the rate of cross slope applicable to the traveled way is influenced by drainage needs. The normal cross slope of the traveled way is 2.0 percent and shall not be less than 1.5 p
41、ercent. When three or more lanes are inclined in the same direction, or in areas of intense rainfall, refer to AASHTOs Green Book for additional guidance. Paved shoulders should have a cross slope in the range of 2.0 to 6.0 percent but shall not have a cross slope less than the cross slope of the ad
42、jacent traveled way. The cross slope break between the traveled way and the shoulder on the high side of superelevated curves should not exceed 8 percent. Medians Medians in rural areas in level or rolling topography should be at least 50 ft (15 m), and preferably 60 ft (18 m), wide. Medians in urba
43、n or mountainous areas shall be wide enough to accommodate the left shoulder width plus the space needed for a barrier. Wider medians may be needed for drainage and may provide flexibility to accommodate future widening for additional travel lanes. Refer to the current edition of AASHTOs Roadside De
44、sign Guide for guidance on barrier installation in the median. Median areas should not be drained across travel lanes. Refer to the AASHTO Drainage Manual, Volume 1 Policy for more information. Roadside Design The clear zone provided should be determined through application of the procedures in the
45、AASHTO Roadside Design Guide. Objects that cannot be made to be breakaway or yielding, such as walls, piers, and abutments, should be shielded by installation of crashworthy barriers or attenuators. Depressed Interstates in urban areas have more restrictive rights-of-way which may need retaining wal
46、ls or bridge piers to be placed within the clear zone. Such walls and piers should be at least 2 ft (0.6 m) beyond the outer edge of shoulder. Retaining walls and pier crash walls should incorporate an integral concrete barrier shape, or they should be offset from the shoulder a sufficient distance
47、to per- mit shielding with a separate barrier. Sideslopes Sideslopes within the clear zone are typically 1V:6H or flatter and should not be steeper than 1V:4H. Where slopes steeper than 1V:4H are used within the clear zone, refer to the current edition of AASHTOs Roadside Design Guide for guidance.
48、2016 by the American Association of State Highway and Transportation Officials. All rights reserved. Duplication is a violation of applicable law.6 A Policy on Design StandardsInterstate System Curbs Caution should be exercised in the use of curbs on Interstates. Where curbs are provided, they shall
49、 not be closer to the traveled way than the outer edge of the paved shoulder, shall have a sloping face, and be limited to a height of 4 in. (100 mm). Special care should be taken when curbs are placed next to bar- riers. For more information, refer to the discussion on curb types and their placement in AASHTOs Green Book. Multimodal Accommodations In urban and suburban areas, consideration should be given to providing bicycle and pedestrian accom- modation along the crossroad or reserving sufficient space for suc
