The Research On Optimizationof Combined Urban Transitnetwork Based On Thetime-limited Free Transfer

In recent years, the rapid development of Chinese city and the rapid increase in car ownership resulted in more serious urban traffic congestion. The existing urban transportation system can not meet the growing demand of travel of residents, which directly affected the sustainable development of social economy. Urban transit, as a relatively small investment, quick effect, efficient way of travelling, played a vital role in urban passenger transport and easing traffic congestion.The optimization of comprehensive urban transit network is the key to ensure the healthy development of urban public transport.In this paper, on the base of summarizing the domestic and foreign research results of the optimization of combined urban transit network, the basic theory of the common public transit network optimization model and algorithm and the optimization of urban transit network including urban social economy, land use, road traffic network, public transport investigation, residents’ travel survey and the modle,utility function and forecasting methods of the share rates of urban trasit network were elaborated. For the policy of ‘time-limited free transfer’, in order to make the comprehensive network composed of rail transit and conventional transit more reasonable, taking the total cost minimum of transit network as the goal, and condition of “time-limited free transfer” as a passenger travel cost factor, and considering the constraints of length of single bus route, the non-linear coefficient of route, the overlap coefficient of route, and the number of transfers, the optimization model of comprehensive network composed of rail transit and conventional transit is established. Considering the condition of “Time-limited Free Transfer”, the ant colony algorithm is proved from the accumulation of pheromone and the punishment mechanism, and the algorithm flow of solving the optimization model of rail transit and conventional transit network is given. The model and improved ant colony algorithm provide a new method for optimizing the comprehensive networkcomposed of rail transit and conventional transit.Taking the Qingdao as an example, the work of field tavel survey to get the basic data of residents’ travel and the data was carried and analyzed. On the base of that 6bus routes were chosen which were representative in necessity of optimization for the application of modle and solving algorithm and the optimization results were obtained.The results show that several key indexes of the optimized bus routes were superior to the corresponding index of the initial routes, thus proving the feasibility, rationality and practical value of the optimization model and the improved algorithm based on the time-limited free transfer.