CMSs are playing increasingly important roles in attempts to improve highway safety, operations, and use of existing facilities. CMSs are traffic control devices used for traffic warning, regulation, routing and management, and are intended to affect the behavior of drivers by providing real-time traffic-related information.
The Changeable Message Sign Operation and Messaging Handbook is a consolidation of the most current and best information on the design and display of effective changeable message sign (CMS) messages for incident and roadwork events. The information was obtained from previous CMS message design and display manuals, more recent research reports, and current state CMS operations manuals, operational procedures, and best practices.
The purpose of the Handbook is to provide guidance to assist agencies with improving the design and display of CMS messages and improving CMS operational procedures. The Handbookcontains the process that can be followed and the techniques that are used to develop effective messages.
The lessons learned discussed below are drawn from the guidance provided by the Changeable Message Sign Operation and Messaging Handbook. The information was obtained from previous CMS message design and display manuals, more recent research reports, and current state CMS operations manuals, operational procedures, and best practices. The term changeable message sign (CMS) is synonymous with dynamic message sign (DMS) and variable message sign (VMS). The following lessons learned discussion gives practical guidance on the design of dynamic message signs.
- Provide motorists with early warning messages. Early warning messages give motorists advance notice of slow traffic and queuing ahead and are effective in reducing secondary crashes. When used in freeway work zones, early warning messages also give notice of new detours, changes in detour route, changes in lane patterns, special speed control measures, etc.
- Design DMS messages to be brief, to the point, and have impact. At typical highway speeds, the message posted on a Dynamic Message Sign (DMS) must be presented to motorists in about 8 seconds or less. This translates to 8 words at 55 mph, 7 words at 65 mph, and 6 words at 70 mph. Therefore, the message must count, and the words used must have impact.
- Design effective DMS messages that have the same message elements and presentation order. The following message elements and order should be used in all DMS messages:
- Situation Description - brief description of the situation
- Situation Location - location of the situation
- Effect on Travel - delays, lanes blocked, etc.
- Action – the action that the motorist should take
- One Good Reason for Following Action - usually implied by situation description
- Including these elements will create DMS messages that have more impact and are more effective with motorists.
Following the guidelines presented in the lessons learned discussed above will help to create DMS messages that are more helpful and useful. Additionally, brief, short messages will be safer to read at highway speeds and will likely produce more satisfied customers since they are able to more thoroughly process the information contained in the DMS messages.