A set of procedures is presented for efficiently designing transit timetables with trips that are initiated beyond the route departure point, or terminated before the route arrival point, or both ("short-turn trips"). In practice, transit frequency is determined at the route segment with heaviest load, whereas at other segments the operation may be inefficient because of partial loads (empty seats). Transit schedulers attempt to overcome this problem by manually constructing short-turn trips to reduce the number of vehicles required to carry out the transit timetable. The study presented herein was meant to improve and automate this task by identifying feasible short-turn points, deriving the minimum fleet size required by a given schedule, and adjusting the number of departures at each short-turn point to that required by the load data (provided that the maximum headway associated with passenger wait time is minimized). Other objectives included minimizing the number of short-turn trips while ensuring that the minimum fleet size is preserved and creating vehicle schedules (blocks). A simple example is used throughout to illustrate the procedures developed. This paper appears in transportation research record no. 1221, Research in bus and rail transit operations.
Abstract