The sustainability appeal of urban rail transit

Urban rail transit (URT) has expanded rapidly since the dawn of the century. Here we examine the impact of URT development on bus service supply and usage, auto ownership, and traffic congestion, by applying fixed-effects panel regression to time series data sets compiled for major urban areas in China and the US. We find that URT development is strongly and negatively correlated with auto ownership in both countries, after controlling for standard social-economic and natural/built environment variables. Importantly, the impact transpires only after a URT system reaches a tipping point that sets in motion a network effect. We also uncover strong evidence of cannibalization by URT of bus market share in both countries. However, rather than undermining the supply of bus services, developing URT is strongly and positively correlated with its growth and adaptation. Finally, no de-congestion benefit of URT is detected in the data. In the US where the analysis is performed, URT development is significantly associated with worsening traffic conditions.