With 23% of energy-related carbon emissions coming from transportation, climate change mitigation will require a deep decarbonization of the transport sector.  In China, transport contributes 10% to national carbon emissions as well as contributing to particulate matter (PM_2.5 ) and ozone formation that damage human health, agriculture, and ecosystems. The deployment of alternative energy vehicles (AEVs) powered by non-fossil electricity or green hydrogen fuel cells is a key strategy to decarbonizing the transport sector.  However, a study by C-PREE researchers have found that compact urban development (CUD) also offers demand-side opportunities to reduce emissions by nearly 10%.

CUD is an urban planning strategy for high density environments that prioritizes designs with accessible transit, diverse land use, and pedestrian-friendly infrastructure.  Conducting a meta-analysis of past studies on Chinese cities, C-PREE researchers project that ambitious CUD policies with low AEV deployment and carbon intensive power could reduce on-road CO₂ emissions by 8% and NO_x emissions by 7% in 2050 China.  They also project that CUD policies would reduce ambient air pollution attributable deaths by as much as 25,000 people per year.  

CUD can reduce the demand for private vehicles and decrease emissions from both fuel consumption and the wear of tires, brakes, and roads.  With ongoing urbanization in China, CUD offers a unique opportunity to strengthen climate mitigation efforts and improve human health outcomes.  

“While deploying AEVs is crucial to decarbonizing on-road transport, measures that reduce transport demand are also important but not well understood.” says STEP Ph.D. student and lead author Xiangwen Fu.  “CUD is a good example of tackling the problem from the demand side, and it provides a great opportunity to avoid future carbon lock-in considering the long lifetime of urban land use and infrastructure.”

When coupled with higher AEV deployment and decarbonized energy sources, CUD produces less climate and air quality co-benefits.  But even with 100% AEV deployment, CUD policies would still reduce deaths attributable to ambient air pollution by 5,800 people per year due to reduced tire and brake wear and would reduce vehicle energy use by as much as 10%.    As concluded by the study, CUD can play a complementary role in scenarios with high levels of AEV penetration.  

”Increasing AEV penetration cannot reduce non-exhaust particulate emissions that are associated with vehicle miles travelled rather than fuel consumption,” explains Fu. “Meanwhile, it will increase the demand for electricity, hydrogen, and critical minerals, which have their own environmental impacts. In this sense, CUD can play a complementary role to AEV deployment and thus benefit the environment.”

“Overall our work shows that compact urban development can have substantial benefits for air quality while internal combustion engines continue to be widely used,” says C-PREE faculty member and corresponding author Denise Mauzerall.  “Over the longer term as transport increasingly relies on electric vehicles, CUD will still provide some co-benefits for air quality and human health while providing energy savings and increasing the livability of cities.”

The paper, “Co-benefits of transport demand reductions from compact urban development in Chinese cities,” was co-authored by Xiangwen Fu (School of Public and International Affairs,  Princeton University), Jing Cheng (Department of Earth System Science, University of California, Irvine), Liqun Peng (Energy Markets and Policy Department, Energy Technology Area, Lawrence Berkeley National Lab and School of Public and International Affairs, Princeton University), Mi Zhou (School of Public and International Affairs, Princeton University), Dan Tong (Department of Earth System Science, Ministry of Education Key Laboratory for Earth System Modeling, Institute for Global Change Studies, Tsinghua University, and Denise L. Mauzerall (School of Public and International Affairs and Department of Civil and Environmental Engineering, Princeton University). The paper appeared in Nature Sustainability on February 8th, 2024.