Although the AASHTO policy reflects input and a consensus of all states, it is recognized that differences in state needs exist. States are free to adopt their own design policies and guidelines, or to accept the AASHTO Policy as written. Indeed, contrary to the understanding of many, the AASHTO Policy does not represent a national standard for design of all roads. The adoption and publication of design standards for highways are the responsibility of each state DOT. While practice varies somewhat, for the most part state DOT design manuals and practices closely follow the guidance in the AASHTO Policy. Some states (Arkansas, for example) adopt the AASHTO policy as written for their practice. Most states develop independent design manuals, design charts, procedures, etc. Note, however, that in most cases the technical content of these manuals is very close to or identical to the AASHTO Policy, particularly for basic geometric design elements of the cross section and horizontal and vertical alignment.
The FHWA is by statute responsible for approving the design of highways on the designated National Highway System. Through rule-making, FHWA has adopted the AASHTO Policy as the applicable set of design values and criteria that apply to such facilities. Finally, it is important to recognize that roads under local jurisdiction (owned and operated by counties, municipalities, or townships) may be designed and maintained to different design criteria, depending on the individual owner. Again, practice varies across the country, but many counties and municipalities follow the design guidelines and practices published by their state DOT.
The Manual on Uniform Traffic Control Devices (MUTCD), published by the FHWA, is also a key reference. The MUTCD describes requirements and recommendations for the application and design of traffic control devices, navigational and warning signing, pavement markings, and work zone traffic control devices. Adherence to the MUTCD is a requirement by law.
Source: NCHRP Report 480: A Guide to Best Practices for Achieving Context Sensitive Solutions p. 46
Published: 2002
