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INFORMATION: Use of Changeable Message Sign (CMS) for Emergency Security Messages

Canceled on January 15, 2010; Superseded by the MUTCD, 2009 Edition

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U.S. Department of Transportation
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Subject: INFORMATION: Use of Changeable Message Sign (CMS) for Emergency Security Messages
March 21, 2003
From: Jeffrey F. Paniati
Acting Associate Administrator for Operations; Acting Director, ITS Joint Program Office
Reply to
Attn of:

To: Division Administrators Empty Cell

The Federal Highway Administration (FHWA) recognizes the value of using changeable message signs (CMS) to convey timely and important information to motorists. State and local transportation agencies have used CMS in times of emergency to convey information to motorists, and ongoing activities related to homeland security may introduce additional opportunities to use CMS. However, messages displayed on CMS must continue to be based on good practice. The purpose of this memorandum is to provide guidance on the use of CMS for displaying emergency or security alert messages.

While CMS can be a very effective method of providing information to motorists, they can convey only a limited amount of information and may not be the safest or most effective method in many cases. Therefore, whatever messages are displayed must be readable and understandable by motorists in the amount of time that the CMS can be viewed. Factors such as prevailing travel speeds, letter height, lighting, and roadway geometrics approaching the CMS (i.e., when motorists can see the CMS) must all be considered in developing the messages to be displayed. Also the messages must consider the desired actions or response by the motorists. For example, general messages that are not related to transportation or specific emergency conditions requiring actions by motorists are discouraged. Additionally, it is unsafe to request motorists to write telephone numbers, websites, addresses, or other lengthy information while they are moving. When there is a need to provide extensive information to motorists, it is critical that other types of traveler information based media (e.g., 511, highway advisory radio, web sites) be used, or that the messages displayed on a CMS supplement these other media.

We continue to discourage the display of general public information or other nonessential messages on CMS. As stated in the January 19, 2001, Policy Memorandum, "INFORMATION: Use of Changeable Message Sign (CMS)" (, FHWA supports the use of a CMS as a traffic control device to safely and efficiently manage traffic by informing motorists of roadway conditions and required actions to perform. It is FHWA policy that the appropriate use of a CMS and other types of real-time displays should be limited to managing travel, controlling and diverting traffic, identifying current and anticipated roadway conditions, or regulating access to specific lanes or the entire roadway.

If public agencies decide to display emergency or security alert messages on a CMS, FHWA has determined that this application is acceptable if public agencies have developed policies and procedures that govern the messages that are displayed on CMS and their operation. The public agency policy and procedures relating to displaying emergency or security alert messages on CMS must address the following issues:

  1. The criteria under which CMS will be used for emergency or security alert messages, including the necessary coordination with public safety or security agencies. Formal policies among critical stakeholders (such as law enforcement, security, transportation, and public safety) can be used to establish these agreed upon criteria.

  2. Protocols or hierarchy for prioritizing messages and determining which messages are to be displayed.

  3. Geographic area over which the information is to be displayed, to be determined in cooperation with public safety and security agencies.

  4. Identification of the circumstances under which transportation-related messages, such as lane closures, fog alerts, detours, or other messages that may be needed because of dangerous travel conditions in the immediate vicinity, would preempt emergency or security alert messages.

  5. The criteria that would cause the discontinuation of use of the CMS if the emergency or security alert message creates an adverse traffic impact such as queues, markedly slowing traffic, etc.

  6. Methodology for developing and displaying messages that are appropriate for CMS display including but not limited to standard message sets. Agencies should follow the recommended national CMS practices related to the development, use of text, manner in which messages should be displayed, human factors related to understandability of the messages, and how CMS are operated.

A list of references that identify these recommended national practices is attached. Additionally, the State transportation agencies in the Transportation Management Center (TMC) Pooled Fund Study will be publishing, this summer, a technical reference that will provide guidance on agency policies and procedures governing CMS operation, how to develop and display messages, and operate CMS. Additional information about the TMC Pooled Fund Study and this project is available at:

Finally, questions have surfaced on the linkage between this CMS policy and the Manual on Uniform Traffic Control Devices (MUTCD). Section 2A.07 of the MUTCD states that a CMS shall conform to the principles established in the MUTCD related to the use of signs within the right-of-way of all classes of public highways, and to the extent practical, the design and applications prescribed in Sections 2E.21 (General: Changeable Message Signs), 6F.02 (Temporary Traffic Control Zone Devices: General Characteristics of Signs), and 6F.52 (Temporary Traffic Control Zone Devices: Portable Changeable Message Signs).

Questions regarding this policy statement should be directed to Mr. Jeff Lindley at (202) 366-6726. For further information regarding message content, display, and CMS operation, please contact Mr. Jon Obenberger at (202) 366-2221, or for information on the MUTCD contact Mr. Ernie Huckaby at (202) 366-9064.

Attachment: Recommended National CMS Technical References

Recommended National CMS Technical References

Attachment: Use of Changeable Message Signs (CMS) for Emergency Security Messages
CMS and Lane Use Control Signs:
Effectiveness of CMS Displays in Advance of High-Speed Freeway Lane Closure TRB NCHRP Rpt No. 235 1981
Guidelines on Use of CMS FHWA Rpt No. FHWA-TS-90-043 1991
CMS TRB NCHRP Synthesis No. 61 1997
Manual on Real-Time Motorist Information Displays FHWA Rpt No. FHA-1P-86-016 1986
Assessment of CMS Technologies FHWA Rpt No. FHWA-RD-87-025 1986
Changeable Message Sign Visibility FHWA Rpt No. FHWA-RD-94-077 4/1996
CMS A Driver Preference Survey Ont. Ministry Transport Rpt No. FHWA-15F 88-03 12/1988
Guidelines on the Use & Operation of CMS TTI FHWA-TX-92-1232-9 11/1992