Manual on Uniform Traffic Control Devices (MUTCD) arrows logo

Interpretation Letter 6(09)-42 (I) – Signing for Rerouting Due to Traffic Incidents

PDF Version, 1.1MB
PDF files can be viewed with the Acrobat® Reader®.
Contact Information: Operations Feedback at

DOT Logo

U.S. Department of Transportation
Federal Highway Administration


INFORMATION: MUTCD – Official Ruling No. 6(09)-42 (I) – Signing for Rerouting Due to Traffic Incidents

Date: April 21, 2017


Mark R. Kehrli
Director, Office of Transportation Operations

In Reply Refer To:


Federal Lands Highway Division Engineers
Division Administrators

Purpose: The purpose of this memorandum is to clarify the Federal Highway Administration's (FHWA) policy on guide signing for rerouting traffic around highway traffic incident sites. This interpretation is based on the provisions of the 2009 edition of the Manual on Uniform Traffic Control Devices for Streets and Highways (MUTCD).

Background: Many agencies have established alternative routings to divert around traffic incidents as part of their transportation incident management plans. These routings can be particularly helpful to motorists to navigate around congestion or closures due to occurrences in locations that are susceptible to traffic incidents. The effect of a traffic incident in a corridor that experiences high traffic volumes might be a significant degradation in mobility in the region due to a temporary reduction in capacity at the incident site. Delays caused by this capacity constraint can result in traffic exiting the highway onto the local system in search of an alternate route. The Pennsylvania Department of Transportation implemented permanently signed "color detours" starting in the late‑1990s for this purpose. More recently, the New York State Department of Transportation implemented a similar system, but used simple guide signs with a lettered designation for each rerouting; no special designs or colors were used. A system of permanently signed, lettered routings to bypass incidents was also installed on the West Virginia Turnpike. Other agencies have implemented differing systems for the same purpose and there now exists a variety of non‑uniform devices in practice to address the same traffic control need.

The MUTCD defines a traffic incident management area as the area that extends from the first warning device deployed to a point where vehicles are downstream from the incident and have returned to the original lane alignment.1 The primary function of these traffic control devices is to establish a "well-defined path to guide road users through the incident area [that] will serve to protect the incident responders and those involved in working at the incident scene…and will preclude unnecessary use of the surrounding local road system."2 Thus, the purpose of temporary traffic control for traffic incident management is to provide the motorist with warning and guidance on the approach to and around the incident site while responders manage the incident and the road on which the incident has occurred remains open to traffic. The temporary traffic control devices and procedures provided in Chapter 6I of the MUTCD apply to incidents lasting up to 24 hours. Temporary traffic control for conditions lasting longer than 24 hours is governed by the other Chapters within Part 6 of the MUTCD.3

Among the practices that have been observed or considered are the following:

Repurposing or Adaptation of Evacuation Route (EM-1 Series) Signs.
Emergency Management signs are reserved for emergencies involving disasters that might require evacuation of the surrounding population.4 The use of the unique design
of the Evacuation Route sign or similar route marker form with a different legend to guide traffic around traffic incidents or other types of detours is not appropriate. Just as particular sign shapes or colors are reserved for specific uses to facilitate recognition, the circular blue background of the Evacuation Route sign is reserved exclusively for routing evacuations away from a potential disaster area. The unique form of this sign provides for instant recognition in an evacuation situation. Alteration of the legend for other applications compromises the integrity of an evacuation route system by debasing the recognition effect of these signs.

Orange or Fluorescent Pink on Permanent Signs.
Orange is reserved for temporary traffic control.5 It is used on signs that are deployed on a temporary rather than permanent basis to address temporary traffic patterns and distinguish signing for the temporary conditions from those for permanent conditions.

Fluorescent pink is reserved for incident management,6 which is a specific type of temporary traffic control that involves the period of first response. Specifically, fluorescent pink is used on signs that are temporarily deployed around a traffic incident to guide traffic through the incident site on the roadway where emergency responders are present during the first 24 hours.

Permanently installed, manually operated blank-out signs that have been used for this purpose have had a tendency to remain deployed even after an incident has cleared. In part, this phenomenon is due to the desire for detours to remain posted to address congestion resulting from capacity issues rather than incidents that involve responders. Therefore, blank-out signs that use orange or fluorescent pink and are intended to be displayed during an incident are not recommended for this purpose due to their inability to be controlled remotely and be displayed only during an incident.

ALTERNATE (M4-1 Series) or BY-PASS (M4-2) Auxiliary Signs or Designations.

The purpose of the Alternate and Bypass auxiliary designations is for an established alternative route7 that is officially designated and mapped with such a route number and auxiliary designation. An alternative route is posted with the auxiliary designations of ALTERNATE (or ALT), BUSINESS, BY‑PASS, or TRUCK. The designation of alternative routes in the U. S. highway system is approved by the American Association of State Highway and Transportation Officials (AASHTO).

The Interstate highway system does not provide for designated alternative routes because of the significantly greater consistency in design standards for Interstate highways that does not necessarily exist for non-Interstate routes. Instead, auxiliary routes within the Interstate system are designated with a three-digit route number signifying connectivity and inclusion within the Interstate System. In the relatively rare instances that a specific class of vehicles is restricted from an Interstate route, regulatory and guide signs would inform and direct that traffic to use other routes to rejoin the Interstate at a downstream location. The rerouting might or might not be along another Interstate route.

Off-Interstate Business routes provide connectivity between the Interstate system and non-access-controlled roadways in business or commercial districts. However, these routes are not part of the Interstate system. The Off‑Interstate Business route designations are also assigned by AASHTO because of the relation to their parent Interstate routes. While the Off-Interstate Business Loop rejoins the Interstate highway at a downstream interchange, it is not designated or signed as an alternative route as established by the provisions of MUTCD §§ 2D.16 et seq.

Because of the established and specific meaning of the ALTERNATE, BY‑PASS, and similar alternative route auxiliary signs that mark the officially designated alternative routes that are shown on official maps, it is not appropriate to use these designations on permanent signing for the occasional incident that might divert traffic onto the local highway system.

DETOUR (M4-8 through M4-10) Auxiliary and Directional Signs or Designations.

Detour signing is for rerouting traffic around a temporary traffic control zone. The signs are in place only for the duration of the activity necessitating the detour. When the activity has concluded and traffic is no longer detoured, the signs are then removed. Similar to the inappropriate use of the colors orange and fluorescent pink on signs that are permanently displayed to traffic, the use of Detour signs on a permanent basis contravenes the provisions of the MUTCD.

Conclusion: It is the official interpretation of the FHWA that permanent signs that guide traffic on diversion routes around recurring or occasional traffic incident locations use a standard form of guide sign with a white legend on a green background. If enhanced conspicuity is desired for those signs, then the provisions of MUTCD § 2A.15 may be used. A portion of the legend identifying the purpose of the sign may be set on a yellow panel within the guide sign to facilitate recognition within the system of signs. The colors orange and fluorescent pink are reserved for temporary signs related to temporary traffic control, with fluorescent pink being specifically reserved for short‑duration traffic incidents as described herein. Signs using these colors are not intended to be deployed or displayed on a permanent basis.

For recordkeeping purposes, this interpretation has been assigned the following Official Ruling number and title: "6(09)-42 (I) – Signing for Rerouting Due to Traffic Incidents." Please direct any inquiries regarding this information to Mr. Marty Calawa,, or Mr. Eric Ferron,, of the MUTCD Team.

For information on Work Zone Management programs, please contact Mr. Paul Pisano,, Team Leader for Road Weather and Work Zone Management. For information on Traffic Incident Management programs, please contact Ms. Kimberly Vasconez,, Team Leader for Transportation Incident and Events Management.


Associate Administrators
Acting Chief Counsel
Chief Financial Officer
Directors of Field Services
Director of Technical Services

MUTCD § 6I.01. [Return to note 1]

MUTCD § 6I.02. [Return to note 3]

MUTCD Ch. 2N. [Return to note 4]

MUTCD § 1A.12. [Return to note 5]

MUTCD § 2D.16. [Return to note 7]