Environmental sustainability of urban expansion: Implications for transport emissions, air pollution, and city growth

• Suburban growth leads to reducing nature accessibility for the existing population. • Suburban growth gives higher CO2 and NOx emissions from traffic. • Compact development reduces emissions but increase population exposure in city centre. • Traffic abatement measures were most effective in the compact city scenario. This study examines the environmental impacts of urban growth in Warsaw since 2006 and models the implications of future urban development for traffic pollutant emissions and pollution levels. Our findings demonstrate that, over the past two decades, urban sprawl has resulted in decreases in accessibility to public transport, social services, and natural areas. We analyse CO 2 traffic emissions, NO 2 concentrations, and population exposure across urban areas in future scenarios of further sprawling or alternative compacting land-use development. Results indicate that a compact future scenario reduces transport CO 2 emissions and urban NO 2 levels, though increases in population density raise exposure to air pollution. A sprawl future scenario increases CO 2 and NO x emissions due to longer commutes and congestion, and NO 2 levels increase up to 25% in parts of the city. Several traffic abatement strategies were simulated, and in all simulations a compact city consistently yields the largest reductions in CO 2 emissions and NO 2 levels, implying that the best abatement strategy for combating negative consequences of sprawl is to reduce sprawling. In both city layouts, network-wide improvements of public transport travel times gave significantly reduced emissions. Combined, our findings highlight the importance of co-beneficial urban planning strategies to balance CO 2 emissions reduction, and air pollution exposure in expanding cities.