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U.S. Department of Transportation

Federal Highway Administration

Subject: INFORMATION: Use of Changeable Message Sign (CMS) Date: January 19, 2001
From: Christine M. Johnson
Program Manager, Operations
Director, ITS Joint Program Office
Reply to
Attn. of:
To: James A. Cheatham
Division Administrator (HDA-PA)
Harrisburg, Pennsylvania

Thank you for your correspondence regarding the operation of a CMS. Section 2A.07 of the Manual on Uniform Traffic Control Devices (MUTCD) requires 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 6.F.02 and 6F.52. Section 2E.21 of the MUTCD specifies that "Changeable message signs shall display pertinent traffic operational and guidance information only, not advertising."

The 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. 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. A national survey of 26 transportation agencies in 1997, indicated that 77 percent had a policy of displaying messages only when unusual roadway conditions are present, leaving the CMS blank during other times.

The use of a CMS for the display of general public information or other nonessential messages is discouraged. Only essential messages should be displayed on a CMS. As per MUTCD

Section 1A.01 "Guide and information signs are solely for the purpose of traffic control and are not an advertising medium."

The content of a CMS message should be based on requiring the motorist to take an action. However, operational, road condition, and driver safety focused messages are acceptable to be displayed on a CMS. If driver safety focused messages are to be displayed on a CMS, they should be kept current and relate to a specific safety campaign. The period of time that a specific messages is displayed for a safety campaign should be limited to a few weeks. Motorists tend to ignore messages that are displayed for long periods of time.

The improper operation and display of outdated or inaccurate information on a CMS has the potential to adversely affect traffic flow. Inaccurate, incomprehensible, or inappropriate information displayed on a CMS can also cause motorists to question the credibility and ignore all CMS messages. The CMS message should be continuously updated to display the action required by motorists, or to present essential information related to either the current or expected future roadway conditions.

The CMS can convey only a limited amount of information. When there is a need to provide extensive information to travelers, it is critical that the messages displayed are used in conjunction with other traveler information media. Agencies should follow the recommended national CMS practices related to the development, the use of text, and the manner in which messages should be displayed. A list of the key technical references that identify these recommended national practices is attached. Also, attached for your reference is a report that has summarized some of these practices.

If State and local agencies decide to use a CMS, a corresponding commitment must also be made to provide the necessary resources to effectively manage and operate each device, in-real time in response to changing roadway conditions. Agencies are strongly encouraged to develop and maintain both regional and agency specific policies, standards, and procedures that govern the operation of both permanent and portable CMSs. This framework should provide the direction related to the design, product specifications and standards, implementation, maintenance, operations manual, allowable messages, methodology used to develop messages, standard words and abbreviations, manner to display messages, and conditions or criteria that correspond to the use of specific messages.

If you need any further assistance or information related to CMSs, please contact
Mr. Jon Obenberger at (202)366-2221. For information related to the MUTCD, please contact
Mr. Ernie Huckaby at (202)336-9064.


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