Manual of Traffic Signs

From the American Association of State Highway and Transportation Officials (AASHTO)


(Adopted August 14, 1957, Revised August 10, 1973)

The National System of Interstate and Defense highways known as the "Interstate System" will be a part of the State Highway systems of the several States and the District of Columbia and will therefore be maintained, operated and policed by those jurisdictions. It therefore becomes the responsibility of the several states to mark and number the System.

Since these highways join centers of population and defense establishments and join with the major international highways at the Mexican and Canadian borders, they constitute a nationwide network of the most important highways; therefore for the convenience of the motorist there must be continuity and a uniform pattern of marking and numbering these routes without regard to State lines.

In arriving at a route marking and numbering policy the following guides shall be used by the Association.

  1. The Executive Committee shall determine and assign the numbers to be used in marking the routes of the Interstate System.

  2. No new divided numbers (such as 1-35W and 1-35E, etc.) shall be adopted. Existing divided Interstate numbers shall be eliminated as rapidly as the State Highway Department and the Executive Committee can reach agreement with reference thereto.

  3. That there will be no Interstate route bearing the same number designation as a U.S. Numbered Route in any State.

  4. That sufficient room be left in assigning numbers to the routes of the Interstate System to allow for future expansion of the system and keep the numbering pattern in sequence.

  5. That no area has any vested right to any route number.

  6. That the routes be so marked as to give maximum continuity between major control points, and that dual Interstate numbering be held to a minimum consistent with proper travel guidance.

  7. The U.S. Route numbers may be used in conjunction with Interstate Route markers where the U.S. Route leads into the Interstate Route, follows it for a reasonable distance, and then departs again from the Interstate Route.

  8. That Interstate Highway patterns in urban areas be carefully numbered and marked for the safety and convenience of the traveling public, and to insure uniformity of practice that each State Highway Department is to submit its plan of numbering and marking of such urban areas to the executive committee for approval prior to the erection of markers.

  9. That a distinctive, easily recognized route marker - shape, color and sizes be adopted and universally used.

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Updated 15 September 2010 (coding)

Scripting: Richard C. Moeur
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