Estimating Phase Duration for SPaT Messages

Abstract

A signal phase and timing (SPaT) message describes the current phase at a signalized intersection for each lane, together with an estimate of the residual time of that phase. Accurate SPaT messages can be used to construct a speed profile for a vehicle that reduces its fuel consumption as it approaches or leaves an intersection. This paper presents SPaT estimation algorithms at an intersection with a semi-actuated signal, using real-time signal phase measurements. The algorithms are evaluated using high-resolution data from an intersection in Montgomery County, MD, USA. The algorithms can be readily implemented at signal controllers. This paper supports three findings. First, real-time information dramatically improves the accuracy of the prediction of the residual time compared with the prediction based on historical data alone. Second, as time increases, the prediction of the residual time may increase or decrease. Third, as drivers differently weight errors in predicting “end of green” and “end of red,” drivers on two different approaches may prefer different estimates of the residual time of the same phase.