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The primary US guidance is found in A Policy on Geometric Design of Highways and Streets published by the American Association of State Highway and Transportation Officials (AASHTO). [2] Other standards include the Australian Guide to Road Design Archived 2011-11-09 at the Wayback Machine, and the British Design Manual for Roads.
Manual for Assessing Safety Hardware (MASH), crash testing criteria for safety hardware devices for use on highways; it updates and replaces NCHRP Report 350. In addition to its publications, AASHTO performs or cooperates in research projects. One such project is the AASHTO Road Test, which is a primary source of data used when considering ...
[1] [3] [2] The HCM has been a worldwide reference for transportation and traffic engineering scholars and practitioners, and also the base of several country-specific capacity manuals. The most-recent version, the Highway Capacity Manual, Seventh Edition: A Guide for Multimodal Mobility Analysis was released in January 2022. [ 4 ]
Unless its author has been dead for several years, it is copyrighted in the countries or areas that do not apply the rule of the shorter term for US works, such as Canada (70 pma), Mainland China (50 pma, not Hong Kong or Macau), Germany (70 pma), Mexico (100 pma), Switzerland (70 pma), and other countries with individual treaties.
The following section pertains to only North American highway LOS standards as in the Highway Capacity Manual (HCM) and AASHTO Geometric Design of Highways and Streets ("Green Book"), using letters A through F, with A being the best and F being the worst, similar to academic grading.
The AASHTO Soil Classification System was developed by the American Association of State Highway and Transportation Officials, and is used as a guide for the classification of soils and soil-aggregate mixtures for highway construction purposes.
Existing bridges can remain part of the Interstate system if they have at least 12-foot-wide (3.7 m) lanes with 3.5-foot (1.1 m) shoulder on the left and a 10-foot (3.0 m) shoulder on the right, except that longer bridges can have 3.5 feet (1.1 m) shoulders on both sides. For all bridges, the railing should be upgraded if necessary.
Typically on straight road sections, the drainage gradient is at least 1–3% due to the normal cross slope of 1–3%. In curved sections the drainage gradient is higher, and may often reach 5–12% due to superelevated CS that may reach 5–8% in areas with icy roads and up to 12% in areas without icy roads.