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A changeable message sign (CMS) is a traffic control device with the flexibility to display a variety of messages. Thus a CMS can be adapted to the needs of work zone traffic control as conditions change. The CMS should be used in conjunction with conventional signs, pavement markings, and lighting. CMS’s have a wide variety of applications in work zones, some of which are:
- Speed control,
- Warning of road closures,
- Accident management,
- Notice of width restrictions,
- Advisories on construction scheduling,
- Advisories on traffic delays, and
- Warning of adverse conditions.
A CMS should be used only when a conventional post-mounted or skid-mounted sign would not be adequate. Frequent and prolonged use of a CMS will diminish its effectiveness.
The message panels on the CMS usually contain room for 3 lines of eight characters each. The message panel is visible from about one-half mile. Individual characters can be seen from 850 feet (260 meters) under normal conditions. Drivers need approximately one second per word to comprehend a message.
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