Independent thesis Advanced level (professional degree), 20 credits / 30 HE credits
The growing congestion problems in big cities result in growing need for public transport services. In order to attract new users, public transport operators are looking for methods to improve their performance and level of service. Service reliability is one of the main
objectives of public transport operators. Various sources of service
causebus bunching: buses from the same line tend to bunch together due to a positive feedback loop, unless control measures are implemented. The most commonly used strategy for preventing service irregularity is to define holding points along the bus route. The design of the holding strategy involves the determination of the optimal number and location of holding points, as well as the holding criteria. These strategies are classified to schedule- or headway-based. Previous studies showed that headway-based strategies have the potential to improve transit performance from both passengers and operators perspectives.
This thesis analyzes the performance of optimization algorithms when solving the holding problem. The optimization process involves the determination of time point location for a given headway-based strategy. The evaluation of candidate solutions is based on a mesoscopic transit simulation. The input data for the simulation corresponds to the bus line number 1 in Stockholm city.
The objective function is made up of the weighted sum of all time components that passengers experience: in-vehicle riding time, dwell time, waiting time at stop and on- board holding time.The optimization was carried out by greedy and genetic algorithms. In addition, a multi-objective function that incorporated the performance from the operator perspective was solved using a multi-objective genetic algorithm.
The results demonstrate the potential benefits from optimizing the location of time point stops. The best solution results in an improvement of around 11% in the objective function value. Interestingly, the results indicate that wrongly chosen time point stops can yield transit performance that is worse off than having no holding control.
2011. , 91 p.