In the Engineering Building, Room 315

Abstract: Signal priority applications in the U.S. tend to be timid about giving priority to buses, because if they interrupt the green period of a competing traffic stream, they have no means of compensating that stream in the next signal cycle (by giving it a longer green period). Common restrictions set up to protect cross streets include preventing a priority interruption in consecutive signal cycles, having short extension intervals, and inhibiting priority when traffic is heavy on the cross street. In addition, most priority applications are limited to one or two simple control tactics, green extension and early green. As a result of these limitations, transit signal priority often falls far short of its potential, saving buses 3 seconds or less per intersection. We show how by using multiple intelligent signal priority tactics, in which traffic is aggressively interrupted but also compensated in the following cycle, large benefits can accrue to transit operations without any undue effect on general traffic. In a simulation study of four traffic signals around a large bus terminal in Boston, we found that average delay per bus could be reduced by almost 20 seconds per intersection with no change in average motorist delay.