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Official Ruling No. 2(09)-174 (I) — Uses of and Nonstandard Syntax on Changeable Message Signs

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U.S. Department of Transportation Federal Highway Administration

Subject: INFORMATION: MUTCD – Official Ruling No. 2(09)-174 (I) – Uses of and Nonstandard Syntax on Changeable Message Signs Date: January 4, 2021
From: Mark R. Kehrli [DIGITALLY SIGNED]
Director, Office of Transportation
In Reply Refer To:
To: Federal Lands Highway Division Directors
Division Administrators
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Purpose:  The purpose of this memorandum is to provide an official interpretation of the provisions of the 2009 edition of the Manual on Uniform Traffic Control Devices for Streets and Highways (MUTCD) related to changeable message sign messaging.  Specifically, we have been asked whether the MUTCD provides for displays on changeable message signs (CMS) that use unconventional wording typically not found on standard signing and how public input into the development of CMS messages may be used.  This information will clarify the provisions of the MUTCD and will assist States and local agencies in ensuring that their traffic control devices will promote the safe and efficient utilization of the highways.

Background:  A CMS can be an effective tool to provide real-time traffic regulatory, warning, or guidance information to the traveling public. In most cases, the messages displayed on CMS are related to traffic delays, travel times, lane closures, rerouting due to traffic incidents, and similar strategies to manage traffic actively on the highway system.  With few exceptions, the MUTCD limits the use of CMS to the display of traffic operational, regulatory, warning, and guidance information.1  Chapter 2L of the MUTCD contains information on all the general types of messages allowed on CMS.

A determination of whether a specific CMS message is suitable begins with consideration of the fundamental principles common to all official traffic control devices:

Traffic control devices or their supports shall not bear any advertising message or any other message that is not related to traffic control.2

In addition, for a traffic control device to be effective, it should meet the following characteristics:3

  1. Fulfill a need;
  2. Command attention;
  3. Convey a clear, simple meaning;
  4. Command respect from road users; and
  5. Give adequate time for proper response.

It is when these five traffic control device principles are engineered into the design, placement, and use of a CMS that it is most effective.  When one or more of these principles is compromised, so, too, is the effectiveness of the CMS.

Similarly, it has been shown that inappropriate or excessive use of a traffic control device can diminish its effectiveness:

A standard device used where it is not appropriate is as objectionable as a non-standard device; in fact, this might be worse, because such misuse might result in disrespect at those locations where the device is needed and appropriate.4

The application of this principle to CMS becomes even more complex as it can refer to the location of the CMS itself, the frequency of display of messages on the CMS, the content of the message displayed, or combinations thereof.

The following illustrates the application of the five principles of an effective traffic control device as they apply to CMS:

  1. Fulfill a need.  Signs fulfill a need by providing regulatory, warning, or guidance information to the road user at the point that information is needed to ensure safe and efficient operation.  The primary purpose of CMS is to provide relevant information on changing highway traffic conditions.  To meet this need, these signs are most often located in advance of major junctions, before areas prone to incidents or adverse road‑weather conditions, and in areas of recurring congestion on facilities with higher volumes and speeds where driver workload demands are high.  Thus, the need to display a message is determined in response to nonpermanent or temporal factors.
  2. Command attention.  By their nature of displaying an illuminated message and, often, by their placement to take advantage of long viewing distances and in an overhead position, electronic CMS tend to capture the attention of the road user. 
  3. Convey a clear, simple meaning.  Clear and simple messages are easy to read and comprehend with only short glances away from the roadway, resulting in minimal visual and cognitive distraction from the driving task.  The use of witticisms, colloquialisms, and popular culture references that target or are comprehended only by a limited segment of the population is not consistent with a clear, simple meaning for all.  Instead, these messages rely on hidden meanings or targeted cultural knowledge to understand the message.  Similarly, the use of newly coined terms (neologisms), words combining the meanings of two words or blending of sounds (portmanteaus), metadata tags ("hashtags"), electronic shorthand ("Internet slang"), and other forms that do not use conventional syntax do not convey a clear, simple meaning to many road users.
  4. Command respect from road users.  Respect for CMS is gained through the posting of information that is relevant to all road users at the location and time it is displayed.  Just as important, CMS messages also command respect through the consistent use of simple, official language and design.  The use of colloquialisms, popular culture references, and other types of indirect or potentially esoteric messaging tends to diminish respect of a CMS as a traffic control device because of its unauthoritative tone and its similarity to promotional advertising that employs a similar approach.
  5. Give adequate time for proper response.  The use of nonstandard or unconventional syntax in a message often results in significantly longer times for the observer to recognize and process.  Further, if comprehension of such a message is poor, then a significant portion of drivers will not respond accordingly or might respond unpredictably, negating any potential benefit that might be gained.

It is important to recognize that the non‑static nature and advanced technological capabilities of CMS still require adherence to the principles that govern other types of official traffic signs whose messages do not change.  While many of the criteria specific to CMS are stated in Chapter 2L of the MUTCD, it is not an independent or comprehensive Chapter unto itself.  Other criteria, such as background and legend color, for example, are stated in Chapter 2A and apply to CMS.

Similarly, the format, content, and amount of legend displayed on CMS should be based on scientific principles that account for the human factors that include the information processing capabilities of the road user, habituation, and credulity.  These principles should not be relegated to lesser importance simply because of the procedures by which the CMS are operated or because of the attractiveness and versatility of their capabilities.  For those cases in which a new technology exists, but appears not to be addressed in the MUTCD, the official interpretation and official experimentation provisions5 of the MUTCD apply.

Effective and Safe Uses of CMS

The primary purpose of CMS is for the display of traffic operational, regulatory, warning, and guidance information.  Other messages allowed by the MUTCD include traffic safety campaigns (by contrast with active warning messages of downstream conditions) and non‑commercial messages related to improving traffic conditions such as those providing information on alternative means of transportation, electronic toll collection, or carpooling. In addition, the display of emergency and homeland security messages, and America's Missing: Broadcast Emergency Response (AMBER) alerts, is also allowed in the relatively rare instances when specific conditions are met.  Primarily displaying relevant traffic-related messages of changing conditions due to congestion, incidents, weather, etc., will help to condition the motoring public to expect a message pertinent to them during those times.  In contrast, excessive display of messages not relevant to traffic operational, regulatory, warning, and guidance information, regardless of the travel or traffic conditions, might adversely impact driver attention to the display of information that is critical to the driving task.  Therefore, the selective and judicious use of CMS for these other purposes will promote the effectiveness of the sign for its primary purpose, which is to display real-time traffic information.  Lastly, adherence to a policy establishing suitable controls that limit the number and duration of non-traffic related messages should make the signs less prone to requests to use them for inappropriate purposes.

The use of CMS to help promote traffic safety is becoming increasingly popular among States and transportation agencies.  It is recognized that CMS can be an effective means of further propagating traffic safety campaign messages directly to the motoring public in a cost-effective manner.  However, to ensure safety and effectiveness as a traffic control device, it is expected that CMS will be used judiciously for the display of safety messages, and that those messages will be derived from larger safety campaigns that rely on other media as their principal means of communicating the campaign message.  These other media generally include, but might not be limited to, such outlets as television, radio, and Internet advertisements; 511 travel information system and Highway Advisory Radio messages; displays in rest areas; and mailings with motor vehicle registrations.  The CMS display, if used as part of a traffic safety campaign, should be a supplement to the broader national or State-level campaign.  In addition, a safety campaign, such as seat-belt use or prevention of impaired driving, should include active enforcement as a primary element of the campaign.

Design of Sign Messages

Principal Uses of CMS

The MUTCD lists several uses of CMS.  These uses are consistent with the uses of traffic control devices in general throughout the rest of the MUTCD and, with two special exceptions, are related to traffic control. The public has now developed a confidence in the operational capabilities of CMS and has come to primarily expect that information relevant to travel conditions will be displayed on them in the event of unexpected conditions.

These two uses remain the principal function of CMS.  Any other uses, to the extent that they are allowed, are considered secondary.

Acceptable Secondary Uses of CMS

Consistent with the principles articulated in the MUTCD, CMS are not intended for promotional purposes or messages that are unrelated to traffic control. Limiting the uses of CMS to messages primarily related to traffic control is expected to help transportation agencies preserve the effectiveness of the sign and its primary function as traffic control devices whose messages adhere to established criteria. Among the uses that are inappropriate for CMS are the following:

Conclusion: Electronic-display CMS, when used judiciously, provide important, real-time information to travelers for improving the safe and effective utilization of the highways.  Their messages help road users navigate congestion and prepare for other unexpected roadway conditions.  As official traffic control devices, it is important that all the allowable types of messages displayed on these signs adhere to the most fundamental principles of effective traffic control devices, among which are relevance and timeliness, simplicity and familiarity of message, minimization of legend elements and complexity, and consistency with other types of signs.  To maintain the integrity and effectiveness of CMS, prudent judgment should be employed in the determination of the use of CMS as well as the content and syntax of messages displayed thereupon.  The adoption by agencies of sound policies governing the judicious use of these official traffic signs is expected to benefit the motorist by preserving their primary use of relevant and timely messages that help the motorist navigate unexpected or unusual traffic and travel conditions.

For recordkeeping purposes, this interpretation has been assigned the following Official Ruling number and title: "2(09)-174 (I) – Uses of and Nonstandard Syntax on Changeable Message Signs."  Please direct any inquiries regarding appropriate CMS use or message design to Mr. Marty Calawa,, of the Office of Transportation Operations MUTCD Team.

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1 Manual on Uniform Traffic Control Devices for Streets and Highways (MUTCD) 2009 Ed. § 2L.01 ¶ 3 [ Return to Note 1 ]

2 Id.; § 1A.01. [ Return to Note 2 ]

3 Id.; § 1A.02. [ Return to Note 3 ]

4 Id.; § 1A.06. [ Return to Note 4 ]

5 Id.; § 1A.10. [ Return to Note 5 ]

6 See MUTCD § 2E.31. [ Return to Note 6 ]

7 [ Return to Note 7 ]

8 Pub. L. 108-21 (April 30, 2003). [ Return to Note 8 ]

9 See MUTCD § 2A.06. [ Return to Note 9 ]