A Meaningful Approach to Assess Urban Public Transit Development: Disentangle General Agglomeration Effects from Specific Local Impacts

The systematic acceleration of socioeconomic process is an inherent feature of city growth, manifested by the superlinear power law of a wide range of variables with population size. The allometry caused by population agglomeration also exists in the demands of Urban Public Transit (UPT). Therefore, transit ridership systematically expresses general increasing returns to population size. Typically, per capita transit ridership is used to assess UPT development. However, it does not account for the fundamental scaling behavior. As a result, this conventional indicator conflates general agglomeration effects, due to average forces of urbanization, and effects of local polices and measures, independently of population size, thereby leading to an unfair comparison between cities with different size. To address these problems, the authors propose a relative metric that distinguishes the specific local impacts. The indicator of Scale Independent Transit Ridership is obtained by evaluating the distance between the actual value of transit ridership and the average baseline expected by the scaling law. It provides a meaningful way to characterize and rank the UPT development of cities. In contrast, the authors find that the per capita measure tends to underestimate smaller cities and overestimate larger cites. They draw a conclusion that the priority strategy of UPT has made significant achievement in China even with the exclusion of general agglomeration effects. The proposed indicator has proved to be a useful way for unveiling some intriguing patterns between transit demands and some urban indicators, which were not properly addressed by the regression on a per capita basis.