Variable-message sign

A variable- (also changeable-,electronic-, or dynamic-) message sign, often abbreviated VMS, CMS, or DMS, and in the UK known as a matrix sign, is an electronic traffic sign often used on roadways to give travelers information about special events. Such signs warn of traffic congestion, accidents, incidents, roadwork zones, or speed limits on a specific highway segment. In urban areas, VMS are used within parking guidance and information systems to guide drivers to available car parking spaces. They may also ask vehicles to take alternative routes, limit travel speed, warn of duration and location of the incidents or just inform of the traffic conditions.

VMS's were deployed at least as early as the 1950s on the New Jersey Turnpike. The NJ Turnpike's signs of that period, and up to around 2012, were capable of displaying a few messages in neon, all oriented around warning drivers to slow down: "REDUCE SPEED", followed by a warning of either construction, accident, congestion, ice, snow, or fog at a certain distance ahead. The New Jersey Turnpike Authority replaced those signs (along with 1990s-vintage dot-matrix VMS's along the Garden State Parkway) with more flexible electronic signs between 2010 and 2016.

The current VMS systems are largely deployed on freeways, trunk highways, or in work zones.

On the interchange of I-5 and SR 120 in San Joaquin County, California, an automated visibility and speed warning system was installed in 1996 to warn traffic of reduced visibility due to fog (where tule fog is a common problem in the winter), and of slow or stopped traffic.

Message Signs were deployed in Ontario during the 1990s in the Greater Toronto Area and are now being upgraded on 400 series Highways in the GTA as well as two pilot secondary highways in northeastern Ontario.

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