FHWA outlines its principles of guide sign messaging for expressways and freeways in MUTCD Chapter 2E. The Chapter establishes that the primary function of guide signs is to provide clear instructions for orderly progress to driver's destinations. Thus, the selection of the destinations is critical and the presentation of those destinations aids in providing clear instructions.
In urban areas, the destinations for service interchanges should be street names, in lieu of cities. The Chapter further defines the requirements for the designation of destinations, amount of sign legend, supplemental signs and various other guide signs commonly found on expressways and freeways.
For conventional roads, FHWA outlines its principles of destination routing for conventional roads approaching freeway interchanges in MUTCD Section 2D.45. Sign sequences approaching interchanges on conventional roads should include a destination sign.
AASHTO publishes the list of control cities for Interstates on their website. This list of control cities is the primary source of destinations for Interstate control cities and is used in conjunction with MUTCD Section 2E.13.02.
The control cities used for signs approaching Interstate routes should be selected from the AASHTO list of control cities for Interstate routes. For approaches within the city limits of a designated control city, the next control city in each direction should be used for the signs.
For interchanges along freeways and expressways, the selection of the destinations for US numbered routes, NC numbered routes, state maintained secondary routes and city maintained routes is established by the NCDOT. The NCDOT principles for destination selection are:
- The number of destinations on any given sign is limited to two, one for each direction of travel from the interchange.
- In the case of overlapping routes, only one destination should be displayed in each direction for each route.
- For routes of regional significance, a destination may be a county seat. Otherwise road names should be used.
- For non-primary routes, the destination shall be the road name
- In either direction of travel along a numbered route, a municipality should not be the destination at more than one exit.
- Unincorporated communities shall not be displayed along freeways or expressways.
- Supplemental guide signs for traffic generators are governed by the policies and practices outlined in NCDOT TEPPL.
- See MUTCD Section 2E.25 for additional information on supplemental guide signs for freeways and expressways.
The intent of these principles is to satisfy the goal of the MUTCD to provide simple and clear instructions. Not following these principles may result in larger, overly complicated signs that take longer to comprehend – which may inhibit decision making by the traveling motorist.