Two Dimensions for Determining and Analyzing the Patterns of the Modal Accessibility Gap in Nanjing, China

Measuring the modal accessibility gap (MAG) is useful for evaluating sustainable transportation development and urban land use. Meanwhile, reducing reliance on private transport (e.g., car use) and raising public transport usage (e.g., bus, metro, light rail, bicycle) is frequently a major goal of transport strategies. Against this background, this study measures the MAG in multi-modal transportation networks from two perspectives: mobility (travel modes and traffic conditions) and proximity (the location and attractiveness of the destination) and describes the methodology developed for an application across the metropolitan area of Nanjing, China. The results show substantial differences between public and private transport in a multi-modal urban network environment based on a realistic “door-to-door” model. In addition, we find that the accessibility advantage of cars is always better than the transit and cycling modes but only from a mobility perspective. The analysis of the sustainability of urban transport should also take account of the location and service capability of the destination and the influence of traffic congestion. The patterns of the smallest MAG scores between the transit and car modes are concentrated along metro and bus routes, and thus they change with traffic fluctuations. On the contrary, the patterns of the smallest MAG scores between the cycling and car modes are concentrated in central urban areas and are thereby affected by traffic conditions including road destiny, river obstacles, and the cross-river channel. Finally, the range of the lowest MAG scores shows a broader distribution in central urban areas in peak hours compared with in off-peak hours.