Modeling and Simulation of Dial-a-Ride and Integrated Public Transport Services
Sammanfattning: Traditional public transport systems are most often insufficient to provide a good transport service to everyone. Especially, it is not always possible for elderly and disabled persons to use the regular system consisting of timetabled services operating along fixed routes. Normally there is some specific service, often called paratransit, offered to these groups of customers. Such transport services provide better service to these customers, but to a higher cost. This thesis considers planning and evaluation of public transport services that are based on the concept of a dial-a-ride service. This kind of service is suitable for elderly and disabled and often operated as a door-to-door service, where customers are served on demand and rides are coordinated via a call-center. The thesis is divided into two parts. In the first part, a modeling system for simulation of dial-a-ride services is presented. It can be used as a tool to study how different ways of operating a dial-a-ride service, affect the performance and efficiency of the service. This system is used to evaluate how algorithmic changes, based on ruin-and-recreate methods, can improve the replanning of already inserted requests, and thereby improve the scheduling. The modeling system is also used to examine the effects of using zone-based distance estimates instead of true, address-based, distances when computing the schedules. The results show that only small differences are found.The second part of the thesis concerns an extension to dial-a-ride services. By combining a dial-a-ride service with a fixed route service, an integrated dial-a-ride service is created, where some part of each journey may be carried out by the fixed route service. An exact mathematical formulation of this problem is presented and it is shown that the formulation is strengthened by valid inequalities, variable substitution and subtour elimination constraints. Simulations of an integrated service are also performed to analyze and evaluate how the attractiveness and operating costs of the service depend on how the demand responsive service is operated.
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