Variable Message Sign (VMS)

Definition and Technical Positioning

A Variable Message Sign (VMS), also known as a dynamic message sign, refers to a highway traffic sign that displays real-time dynamic information such as road, traffic, and meteorological conditions via remote-controlled systems. Unlike static fixed signs, it can dynamically update its display based on real-time traffic conditions, alerting motorists in advance of accidents, adverse weather, roadworks, and traffic congestion ahead to support informed driving decisions. VMS serves as a primary tool for traffic guidance and traveller information services within Intelligent Transport Systems (ITS).

Main Functions

The core function of VMS is to translate dynamic traffic data into clear visual signals for motorists, encompassing road condition alerts (upcoming roadworks, landslide/flood damage, road closures/openings, etc.), traffic status updates (accidents, traffic jams, etc.), and weather advisories (heavy rain, dense fog, snow, icy road surfaces, etc.). By broadcasting these updates, VMS assists in guiding vehicles along optimal routes and balancing traffic flow across the road network, playing a vital role in macro-level traffic management. On expressways, VMS can also interface with Rest and Service Areas to display real-time updates such as EV charging facility status.

Technical Types and Implementation Methods

Based on display technology, VMS is primarily categorised into matrix display, light-guide display, and variable panel selection types. Currently, the most prevalent type is the LED matrix dynamic message board, which selectively illuminates electronically controlled matrix bulbs or LEDs to form required text and symbols. Certain VMS units feature automatic brightness adjustment based on ambient lighting to ensure optimal day and night visibility. In terms of layout format, VMS is divided into text-only boards, graphic boards, and combined text-and-graphic boards, with graphic VMS representing the technology's primary evolutionary direction.

Regarding display colour specifications, according to national standard GB 5768.2-2022, internally illuminated variable message signs use designated colours based on message type: green for general information, yellow for warnings, and red for prohibitory notices. The standard also mandates that VMS must not display non-traffic-related content, should not feature animation effects such as simulation, dissolve, or explosive transitions, and must be switched off when no information is required. Mounting options include post-mounted, cantilever, and overhead gantry structures, typically positioned ahead of expressway exits and entrances, long tunnel portals, and other critical road sections.

Typical Application Scenarios

VMS is widely deployed in traffic management across urban expressways and highways. In Beijing, over 400 dynamic message boards have been installed to support graphical traffic condition displays and travel time estimation. Meanwhile, Anhui Province has piloted a VMS-based "Dynamic Emergency Lane Guidance System" on congestion-prone sections such as the G40 Shanghai–Shaanxi Expressway and G4212 Hefei–Anqing Expressway—when traffic builds up, expressway traffic police authorise lane opening, prompting dynamic guidance displays along the hard shoulder to sequentially show notices such as "Emergency Lane Open to Traffic" or "End of Lane Access", functioning similarly to urban traffic signal lights.

Technology Evolution Trends

VMS technology is progressively integrating with vehicle-infrastructure cooperative systems (V2X). Selected next-generation message boards now incorporate camera modules and predictive algorithms to achieve seamless data synchronisation with autonomous vehicles. On the cybersecurity front, VMS systems are implementing device fingerprint authentication and state cryptographic algorithm encryption to safeguard against unauthorised data tampering. Current research also focuses on the "networked" integration of VMS data—moving beyond isolated standalone units to enable synchronised linkage and coordinated information dissemination across multi-unit VMS networks.