A POLICY ON DESIGN STANDARDS INTERSTATE SYSTEM
|Publication Date:||1 January 2005|
The National System of Interstate and Defense Highways is the most important in the United States. It carries more traffic per kilometer (mile) than any other comparable national system and includes the roads of greatest significance to the economic welfare and defense of the nation. The highways of this system must be designed in keeping with their importance as the backbone of thenation's highway systems. To this end, they must be designed to ensure safety, permanence, utility, and flexibility to provide for predicted growth in traffic.
These objectives can be realized by conscientious attention to design. All interstate highways shall meet the following minimum standards for segments constructed on new right-of-way and segments undergoing complete reconstruction along existing right-of-way. The standards used for horizontal alignment, vertical alignment, and widths of median, traveled way, and shoulders for resurfacing, restoration, and rehabilitation projects may be the AASHTO interstate standards that were in effect at the time of original construction or inclusion into the interstate system. Designs will generally be made to values as high as are commensurate with conditions. Values approaching the minimums here in will be used only where the use of higher values will result in unacceptable social, economic, or environmental consequences.
Design values are presented in this document in both metric and U.S. customary units and were developed independently within each system. The relationship is neither exact (soft) nor a completely 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 and not attempt to convert directly between the two. In addition, all projects, including 3R, or elements of projects that retain existing geometria meeting the minimum standards for the selected design speed in one system of units are considered in compliance with comparable design speed standards in the other.
The current editions of AASHTO's A Policy on Geometric Design of Highways and Streets and the Standard Specifications for Highway Bridges shall be used as design guides where they do not conflict with these standards.