EMAS lane-use and variable message signs

The Expressway Monitoring and Advisory System (EMAS) uses electronic signboards on expressways and selected major arterial roads. The official handbook groups them into travel-time displays (TTDs), traffic-information displays (TIDs), and traffic-sign displays (TSDs) (SPF, Basic Theory of Driving).

TTDs show estimated travel times to selected expressway exits and may show an incident message. TIDs use text and simple graphics to describe conditions ahead, such as an accident, road closure, affected lane, congestion, travel time, or another traffic advisory. A TSD is generally a smaller sign on the expressway centre divider; it uses symbols to show adverse conditions or tell motorists to change lanes (SPF, Basic Theory of Driving).

Common handbook symbols include:

• a red cross, meaning the lane is closed;
• a flashing amber cross, meaning possible obstruction ahead: slow down and prepare to change lane;
• a green arrow, indicating that the lane is open;
• must exit, meaning the expressway is closed ahead and the driver should exit;
• exit closed ahead, meaning use an alternative exit; and
• lane reduction, meaning an obstruction is ahead: slow down and prepare to change lane (SPF, Basic Theory of Driving).

OneMotoring separately tells tunnel drivers to follow overhead lane-use signs and traffic-message signboards. In a tunnel emergency, drivers should not proceed into a lane displaying a red X; a green arrow marks a passable lane (LTA OneMotoring, Driving on Expressways & in Tunnels).

Coverage debt

• The handbook presents examples rather than a complete machine-readable symbol index; this article does not infer meanings for symbols not described by the cited material.

Sources

• SPF, Basic Theory of Driving
• LTA OneMotoring, Driving on Expressways & in Tunnels