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. The content of a CMS message should be based on requiring the motorist to take an action. 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The improper operation and display of outdated or inaccurate information on a CMS has the potential to adversely affect traffic flow.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.