Roads, economy, population density, and CO2: A city-scaled causality analysis

The exploration of the nexus among transport infrastructure, economy, population, and environment would be important for sustainable transport system planning. In this paper, we choose Shanghai as a case, account its transport CO2 emissions from 1989 to 2014 and investigate the causality relationships among variables through Johansen cointegration, multivariate Granger causality tests based on vector error correction model, impulse response functions and variance decomposition. The results of Granger causality tests indicate that road infrastructure development did not contribute to the GDP growth in transport sector, but caused direct increase in transport CO2 emissions and population density. The impulse response analysis confirms the phenomenon that the enhancement of population density will reduce the per capita level of CO2 emissions. The policy implications for reducing the impact of road infrastructures on carbon emissions include the promotion of new energy vehicles and green transport infrastructures, emphasis on the environmentally friendly transport modes, enhancement of city's compactness and population density through the road construction especially in new towns.