Development and evaluation of intelligent bus priority concept

Development and laboratory testing of an intelligent concept for providing priority to buses at signalized intersections without disrupting progression are discussed. The concept used bus position information to predict when in the cycle a bus would arrive at the bus stop and stop line of a signalized intersection and to determine whether a bus needs priority. The strategy used to provide priority was selected on the basis of the estimated arrival time of the bus at the stop line. Priority was provided by using phase extension, phase insertion, and early return strategies without causing the controller to drop from coordination. Implementation of the strategies was accomplished through normal traffic-signal controller commands (such as Ring Force Offs and Phase Holds). Hardware-in-the-loop simulation studies were performed to evaluate the effectiveness of the concept with real traffic-signal controllers. The performance of the intelligent bus priority approach was examined at three volume-to-capacity levels: 0.5, 0.8, and 0.95. Significant reductions in bus travel times were achieved at all three volume-to-capacity levels by using the intelligent bus priority approach. Use of the intelligent bus priority approach resulted in only minor increases in total system stop delay and individual approach stop delays at volume-to-capacity levels of 0.5 and 0.8. The results of the simulation studies performed as part of this study suggested to the researchers that the intelligent bus priority approach could be used at moderate traffic levels (up to volume-to-capacity levels of 0.9 or less) without significantly affecting cross-street delays.