616.3 Changeable Message Signs (CMS)
From Engineering Policy Guide
Changeable message signs (CMSs)are portable signs capable of displaying several messages in a sequence and display pertinent traffic operational and guidance information as well as advise drivers of unexpected work zone traffic and routing situations. Such messages shall be changed manually, by remote control, or by automatic controls. Changeable message signs shall not display advertising. Use of CMSs shall conform to the general principles of the the Manual on Uniform Traffic Control Devices (MUTCD) and the FHWA Guidelines for Changeable Message Sign Messages Manual. If displayed messages include abbreviations, they shall conform to Table 910.3.2.3 and Tables 1-2 and 1-3 of the MUTCD. Messages displayed shall convey pertinent information to assist motorists' driving decisions. Messages shall be conveyed in a standard, non-confusing manner that allows drivers to both perceive and react to the information in a timely fashion.
CMSs can be used to effectively reduce congestion caused by planned events or unplanned incidents such as excessive daily traffic, accidents, detours, construction delays, etc. Once a driver population has gained confidence that messages are reliable and relay pertinent information that assists in reducing delays, CMSs can be used to convey information to alter traffic patterns or modes of transportation.
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616.3.1 Temporary Traffic Control Guidelines
The CMS supplements other work zone signing to advise drivers of unexpected work zone traffic and routing situations or to provide additional information to the driver. CMSs shall not be used to replace or repeat static sign messages. Typical applications for CMSs are:
- Where backups are expected to extend beyond the beginning of the standard sign sequence.
| Related Information |
| Dynamic Message Signs (DMS) |
- Where the speed of traffic is expected to drop substantially.
- Where there are extreme changes in alignment or surface conditions.
- To provide additional advance notice of ramp, lane or roadway closures.
- For incident management.
The proposed location(s) and quantity of CMSs are shown on the TCP. Application and placement guidelines for the CMS are:
- The CMS is typically placed in advance of any other temporary traffic control signing and is not used to replace or repeat other required signing.
- Where used for route diversion, the CMS is to be placed far enough in advance of the work site to allow traffic ample opportunity to exit the affected highway.
- The CMS is normally placed off the roadway shoulder. CMSs shall not be placed in medians. The CMS shall be delineated with channelizer drums.
- Each CMS shall not convey more than two messages. When two signs are needed to communicate multiple messages, they are to be placed on the same side of the roadway, separated by at least 1000 ft.
Radar Speed Advisory Assembly
These devices contain an active display that indicates the speed of each vehicle as it passes the sign. These devices are recommended on divided highways with lane closures, multilane urban or rural resurfacing projects over 5 miles and bridge rehabilitation projects with lane restrictions lasting 30 days or more. These devices shall not be used on routes with a posted speed prior to construction less than 50 mph. Other conditions may warrant the use of this device.
616.3.2 Non-Temporary Traffic Control Guidelines for CMSs (MUTCD Section 2E.21)
Standard. CMSs shall be capable of displaying several messages in a sequence. Such messages shall be changed manually, by remote control, or by automatic controls. CMSs shall display pertinent traffic operational and guidance information only, not advertising.
Support. Because technology for CMSs continues to advance, a specific standard for changeable message signs is not practical. Considerations that influence the selection of the best sign for a particular application include conspicuity, legibility, operation and maintenance of the CMS. This article applies to signs for use on freeway and expressway mainlines. It is recognized that similar signs might be used on ramps and at ramp terminals where smaller letter heights and the number of messages might differ from the provisions of this article.
Guidance. To the extent practical, the design and application of CMSs should conform to the general principles of this manual.
616.3.3 Non-Temporary Traffic Control Guidelines for CMSs along Freeways and Expressways
Refer to 910.3.2 MoDOT DMS Policy for guidance.