Implementing Headway‐Based Reliability Control on Transit Routes

This paper presents the operational issues and results of implementing real‐time headway‐based reliability control along candidate bus routes operated by the Massachusetts Bay Transportation Authority in 1987. The procedure involves holding buses at a control point on the route until a prescribed minimum headway is achieved. Headway‐based control strategies apply to high‐frequency transit routes where headways are sufficiently short that travelers arrive randomly at bus stops without consulting a schedule. It is considered appropriate for correcting service disruptions that have already occurred, or for preventing propagation and further service degradation. The goal of this effort is to improve service reliability as perceived by travelers, as well as to allow for more effective utilization of operator resources. Failure by street supervisors to consistently follow holding instructions and data collection problems involving point checkers hampered the evaluation effort. Nevertheless, it appears that certain routes may benefit from holding actions. Where these improvements are measurable, dramatic operator savings, due to reduced vehicle requirements, may be realized. This depends on the extent to which passenger load, relative to vehicle capacity, may preclude the operator from taking maximum advantage of the derived service benefits.