A SPaT (Signal Phase and Timing) message describes for each lane the current phase at a signalized intersection together with an estimate of the residual time of that phase. Accurate SPaT messages can be used for several purposes:

(1) a vehicle can construct a speed profile that reduces its fuel consumption as it approaches or leaves an intersection;

(2) users can use the current phase to determine who has the right-of- way;

(3) buses, emergency vehicles, trucks, and cyclists can request an “extension” if they determine they cannot reach the intersection during “green”.

The talk will provide a brief introduction to signal timing and describe an algorithm to construct a SPaT message based on historical and real-time signal information.