Public Transport Workforce Sizing Recognizing the Service Reliability Objective

This paper presents a method for determining the optimal number of public transport operating personnel so as to minimize total operating cost subject to a constraint on the minimum level of service reliability. For a given timetable and crew scheduling solution, the number of operators required to be available is known if all service is to be run and no additional (unscheduled) service is required. However, in light of uncertainties about absence rate and incidence (over the day, the week and the year), and the need for extra service as well as the time involved in hiring and training new operators and restrictions against laying off operators once hired, determination of optimal workforce size is a difficult problem. The method proposed involves developing a relationship between the amount of overtime required (to fill in for any manpower deficit which may occur) and the resulting service reliability. A two-stage method is developed which first estimates the optimal number of operators required in each period (typically four-weeks long), and then defines the annual hiring program and vacation allocation plan to minimize the “errors” from the ideal manpower targets in each period. A case study of the MBTA is used to illustrate application of the proposed method.