Integrated design of urban rail transit and bike-sharing system considering route choice varieties in a ring-radial hybrid network

Public transit accessibility can be enhanced by the flexible bike-sharing system. Existing studies on strategic transit design, however, often fail to jointly capture the cooperative and competitive relationships between transit and bike-sharing, especially in cities with ring-radial road networks. This study examines the integrated system of urban rail transit (URT) and bike-sharing (BS) service while travellers can bike to access URT stations or reach destinations directly. The stylized URT network features a hybrid ring-radial structure, with a ring-radial layout in the central area and radial extensions in peripheral areas. A parsimonious continuum method is used to formulate the strategic design model for the integrated system as a mixed integer program. Importantly, the model explicitly incorporates travelers’ route choice, comprehensively examining its varieties for travelers with different origins and destinations. These choices are affected by the spatial relationship between origins and destinations as well as by system design variables, and we analyze the route choice to facilitate an easily solvable optimization model. Numerical experiments demonstrate that a significant proportion of travelers opt for biking directly, especially under low demand conditions (with the proportion up to 40%), but the proportion is low in densely populated large cities. Additionally, a smaller city often features an insignificant central area and very few URT ring lines, regardless of demand levels, due to cost-effectiveness of BS.