Route numbers for Interstate and US routes have been assigned by AASHTO and the FHWA. However, route changes to the Interstate and US numbered routes can be submitted to AASHTO for approval by the NCDOT. Any route modifications to the Interstate system must be approved by the United States Secretary for the Department of Transportation. Any modifications to the US numbered routes must be approved by the Special Committee on U.S. Route Numbering of AASHTO.
FHWA outlines its principles of route numbering in the MUTCD, Section 2D.09
Numbered Highway Systems. In this section, several key points of numbered routes are stated as follows:
- The intent of numbered systems is to identify continuous routes and facilitate travel along those routes.
- Overlapping of routes should be avoided.
- The States have the authority to designate numbered routes within their own jurisdictions.
Section 2D.09 also refers to key AASHTO documents regarding numbered routes:
- Establishment and Development of United States Numbered Highways
- Establishment of a Marking System of the Routes Comprising the National System of Interstate and Defense Highways
These two publications by AASHTO identify the principles of the Interstate and US numbered routes. Also, included in these documents are the procedures to apply for route changes within the system.
The NCDOT has the authority to manage the numbered route system in North Carolina. The NCDOT may apply for route changes and extensions of the existing Interstate and US numbered routes and may develop and manage its own state numbered route network. The NCDOT State Traffic Engineer must initially review all proposed Interstate, US and NC Route changes.
The basic principles of the NCDOT numbered route assignments are:
- Maintain the principles of the FHWA and AASHTO numbered routes.
- Add only logical additions to the existing Interstate and US route system.
- Minimize the number of routes on any given facility.
- Assign the highest order routes, Interstate routes, to high speed, high capacity freeway facilities serving long distance commerce and travel. Interstate designated routes shall meet AASHTO requirements for freeways.
- Assign second order routes, US routes, to high capacity facilities of
regional significance or long distance commerce and travel in rural areas. US designated routes shall meet AASHTO requirements for facility type they are assigned to.
- Assign lower order NC routes to lower capacity facilities of
local significance, or regional significance in rural areas.
- For higher order routes, maintain parallel, lower order, numbered routes for incident management routing where possible.
- Provide continuity with the path traveled by minimizing the number of turns and exiting maneuvers.
- Eliminate or reassign routes that conflict with the principles above.
- Maintain historical route continuity by minimizing requested changes that do not conflict with principles above.
Route Change Guidelines
If an Interstate, US or NC route will be deleted, relocated or established as part of a project a Routing Concept Plan is required. Notify the Regional Signing Engineer as soon as possible since route changes affect several departments and early coordination is key in determining the appropriate route location and design ramifications. The following principles and requirements apply for projects that include route designation changes:
- Approvals required prior to sign Installation:
|Route Type||FHWA||AASHTO||NCDOT Chief Engineer||NCDOT State Traffic Engineer||Division Engineer||Local MPO/RPO|
|Future Interstate||X||X||X||X|| ||X|
|US|| ||X||X||X|| ||X|
|NC|| || || ||X||X||X|
|SR|| || || || ||X|| |
- The meeting for AASHTO approvals occurs only twice year – Spring and Fall.
- For Interstate and Future Interstates route changes, FHWA requires Local MPO or RPO approval prior to submitting the application to AASHTO.
- For US routes, NCDOT requires Local MPO or RPO approval prior to submitting the route change application to AASHTO.
- For NC routes, NCDOT requires Local MPO or RPO approval prior to submitting the route change application.
- A Future Interstate is
not an official Interstate. Future Interstate signs indicate an Interstate is scheduled to be there in the future. An underlying route (SR, NC or US route) is required to be in place until officially an Interstate.
- An Off-Interstate Business Route (Green Shields) is
not an official Interstate. Green Shields indicate the route serves the business area of a city and has a connection to an official Interstate. An underlying route (SR, NC or US route) is required to be in place.
- Additional Off-Interstate Business Routes will not be approved.
- An Interstate must be on the
- The route must meet all
current Interstate System design criteria set by the AASHTO “A Policy on Geometric Design of Highways and Streets" or have approved design exceptions.
- An Interstate will not be accepted by
FHWA until reasonably close to completion.
- The high priority routes in NC are I-42, I-73, I-74, I-87 and the Greensboro Corridor (I-785).
- A high priority route can connect to an Interstate on one end and a NHS route on the other.
- A non-high priority route must connect to an Interstate on both ends.
Future Interstate Requirements
US Route Requirements:
- The route must meet all current design criteria set by the AASHTO “A Policy on Design Standards" or have approved design exceptions.
- US Bypass, Business, or Alternate Routes shall not exist without the regular numbered route.
NC and SR Routes
Connect NCDOT – Traffic Safety - Route Changes
Numbered Primary Routes in North Carolina Document