讲座题目：Optimal Design of Bimodal Transit Corridor with Many-to-Many Demand
讲座内容：It is widely observed in urban areas that major transit corridors often consist of multiple transit systems (e.g., regular street bus, bus rapid transit (BRT), and rail transit) partly or mostly overlapping along the corridor, on which local and express services are simultaneously provided to all transit patrons. Traditional transit corridor design, however, was mainly focused on single transit technology with particular one type of operation strategy, and consequently provided little guidance for seeking the optimal design of a hybrid transit corridor (in terms of the stop locations and headways, for instance). Targeting at long-term transit planning, this paper adopted the continuum approximation method to model the optimal design of a linear bimodal transit corridor with local and express services. Given the many-to-many demand pattern, patrons’ route choices were explicitly considered among 5 types of route options: (1) express only, (2) local only, (3/4) local/express-transfer- express/local, and (5) local-transfer-express-transfer-local. The objective function is established to minimize the generalized system cost, which is the sum of patrons’ cost and transit agency cost. Analytical solutions are presented with regards to 2 types of decision variables/functions: the transit headways (uniform along the corridor), and stop densities (as functions of location at the corridor) of the local and express transits. In the numerical studies, we first demonstrated the effectiveness of the proposed model by illustrating the optimized headways and stop densities (varying with locations) as well as the volume splits among 5 types of routes at equilibrium. We then conducted parametric analysis with respect to the total demand and the corridor length under two generic scenarios (i.e., low- and high-wage cities). The system performances of the optimal bimodal transit systems were compared against that of the conventional single-mode transits (i.e., Bus, BRT, and Rail). The results shown that the bimodal transit systems (particularly the Bus-BRT system) generally outperform the single-model systems at conditions with high demand and at lengthy corridor. Over 5% and 10% cost savings were observed for the bimodal systems under low- and high-wage scenarios, respectively. Lastly, we applied our models to a case study with realistic station-to-station volumes (approximated by continuous density functions) of the No. 1 metro line in Chongqing city (China). The optimal design solutions suggested by the model were compared to the current line configuration. Discussions were provided on possible ways of system improvement.