Editing Variable-message sign (section)

==Movable versions==
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[[File:Cromwell_road_outside_VA.jpg|thumb|Trailer-mounted VMS in central London, England]]
Truck-mounted VMSes (also called Portable Changeable Message Signs or PCMS) are sometimes dispatched by highway agencies such as [[Caltrans]] to warn traffic of incidents such as accidents in areas where permanent VMSes are not available or near enough as a preventive measure for reducing secondary accidents. They are often deployed in pairs so that the second VMS truck can take over when the traffic queue overtakes the first truck, requiring the first truck to reposition further upstream from the queue, to be effective. An optional third truck, the team leader, may be utilized for driving by and monitoring the incident itself, traffic patterns and delay times, to make strategic decisions for minimizing delays—analogous to spotter planes used in fighting forest fires.

Trailer-mounted variable-message signs are used to alter traffic patterns near work zones, and for traffic management for special events, natural disasters, and other temporary traffic patterns. The messages displayed on the sign can be programmed locally on the unit's control panel, or units equipped with a cellular modem can be programmed remotely via computer or phone. Most manufacturers produce trailers which comply with the [[National Transportation Communications for Intelligent Transportation System Protocol]] (NTCIP) which allows the portable trailer to be integrated with an [[intelligent transportation system]]. Trailer-mounted VMS can be equipped with radar, cameras, and other sensing devices as part of a [[smart work zone]] deployment..