Integrated optimization for feeder bus timetabling and procurement scheme with consideration of environmental impact

Undesirable environmental impact of public transport (PT) and saving operational cost are of major importance to deal with. For a design of a new bus line, this plays a significant role on which fleet to purchase. The objectives of this work are to integrate vehicle procurement scheme and timetabling for a new feeder bus line with the constraint of purchasing budget, so as to (i) not only meet passenger demand, but also minimize their waiting time, and (ii) minimize the operator's costs, including the consideration of environmental impact of PT, which can be measured by the penalty function of greenhouse gas emissions. A bi-objective optimization model for a feeder bus line is formulated to minimize operating cost and to minimize passengers' waiting time. Timetables with even and uneven headway as well as single and multiple vehicle types are compared to verify the effectiveness of the proposed model. The solution approach is based on a decomposition heuristic method to tackle the procurement scheme and vehicle assignment, and on a real-number-coding genetic algorithm to generate departure times for each trip. Buses in three different types are considered: a mini electric, a liquefied natural gas, and a hybrid diesel with capacities of 35, 50, and 70 passengers, respectively. A case study in Beijing shows that, compared with the current timetable, the optimized MT-Uneven-headway timetables save 70.4% and 54.2% passengers' waiting time and reduces the total cost by 64.1% and 31.2% for the morning and evening peak hours, respectively, indicating that the integrated method is effective.