Variable message signs

Variable message signs (VMS) are permanently-installed or portable electronic roadside signs operated remotely by traffic management centers (TMC) to post traveler information messages to inform drivers of incidents, travel times, detours, special events, and other useful road conditions or travel information. VMS can be used to post messages required by various demand management and traveler information strategies, including queue warnings, variable speed limits, route choice, and dynamic lane assignment.

VMS Placement

VMS are typically connected to a central location, such as a TMC, where the signs are operated remotely and can be quickly changed to provide current information. VMS are especially useful to display in advance of locations where travelers must take action or make route choice decisions. Because VMS messages can be seen only when drivers pass by, strategic placement of the signs, especially permanently-installed signs, is critical. Portable VMS can be used to display traveler information messages for special events or other temporary conditions, such as road construction.

Message content 

VMS messages must also be concise and clear enough for the drivers to interpret at high speeds. The Manual on Uniform Traffic Control Devices (MUTCD), published by FHWA, provides detailed guidance on appropriate text size, resolution, and message content for the VMS sign based on the expected speed of drivers.

Public service announcements

When not being used to display traveler information, VMS may be used to display public service announcements, including messages about distracted driving, impaired driving, and seat belts. However, because overuse of VMS can lead to drivers ignoring the posted messages, many agencies strictly limit the types of messages that can be displayed, reserving VMS only for critical traveler information or safety messages.