Copyright © IFAC Transportation Systems Chania, Greece, 1997 CREATION OF OBJECTIVE FUNCTIONS FOR TRANSIT NETWORK DESIGN A vishai Ceder and Yechezkel Israeli Transportation Research Institute Civil Engineering Department Technion -Israel Institute o/Technology Haifa 32000, Israel Abstract: This paper describes the basic construction of the objective functions of the transit network design problem and proposes a new approach taking account of both passenger and operator interests. The approach presented combines the philosophy of the mathematical programming approaches with decision-making techniques, so as to allow the user to select from a number of alternatives. The nature of the overall formulation is nonlinear and mixed integer programming. Keywords: Transport, Networks, Optimization, Routing Algorithms, Scheduling Algorithms. 1. INTRODUCTION The problem addressed in this paper is a general one of how to design a new transit network or redesign an existing one, given no a-priori specifications as to the desired network structure. From a practical perspective it is desirable that the route design procedures include interaction and feedback loops between the selection of effective routes and the operational schedule components: Frequency determination and time-tabling along with vehicle scheduling with regard to fleet size. The system generates all feasible routes and transfers which connect every place (node) in the network to all others. From this vast pool of possible routes and transfers, it then generates smaller subsets which maintain network connectivity. For each subset thus generated, the system meets transportation demands by calculating the appropriate frequency for each route. Next, it calculates pre-specified optimization parameters for each subset. Based on the specific optimization parameter desired by the user, it is then possible to 667 select the most suitable subset. The system has been designed as a tool for the planning of future transit networks as well as the maintenance of existing ones. The system ensures flexibility by allowing the user to either input his own data or to run the system automatically. 2. PROBLEM IDENTIFICATION The transit planning process, aimed at efficient transport of origin-<iestination transit-riders, includes four basic elements performed in sequence: (a) Network Route Design: (b) Setting Timetables; (c) Scheduling Vehicles to Trips; and (d) Assignment of Drivers. In order for this process to be cost-effective and efficient, it should embody a compromise between passenger comfort and cost of service. For example, a good match between bus supply and passenger demand occurs when transit schedules are constructed so that the observed passenger demand is accommodated while the number of vehicles in use is minimized.