How to Improve High-frequency Bus Service Reliability through Scheduling

This paper outlines a scheduling process for improving high-frequency bus service reliability based on a model which uses Automatic Vehicle Location and Automatic Passenger Count data. Developing a schedule for high-frequency bus routes involves balancing the costs to the passengers and the cost to the transit agency. Passengers are interested in short travel times and short, reliable waiting times. In order to assess the trade-off between trip speed and reliability, transit planners need to follow a clear scheduling process, which explicitly projects and evaluates the tradeoffs between overall travel time and reliability. The proposed model estimates the cost of any given schedule for waiting passengers, onboard passengers and the transit agency based on the existing variability in running times and headways. The scheduling process involves finding the time point schedule which minimizes the total cost with the help of the model. The model is based on two critical hypotheses: (i) consecutive bus vehicle trips are independent and (ii) consecutive segment running times for a particular bus trip are independent. These two critical hypotheses were shown to be true on two highfrequency bus routes analysed in Chicago; Route 95E and 85. For each route, the schedule which minimises the total passenger cost was determined. The schedules obtained with this generalised cost minimisation approach showed improved reliability and overall passenger service quality – at the same operating cost compared to the current schedules on both routes, as well as compared to traditional approaches. A sensitivity analysis has shown that in most cases the generalised cost minimisation schedule can significantly improve reliability and overall passenger service quality over traditional approaches.