Can ultra-high voltage transmission projects reduce regional carbon emissions? Evidence from 279 cities in China

Ultra-high-voltage (UHV) transmission, a key new infrastructure project, addresses China's spatial mismatch between energy supply and demand, supporting energy reform and the “dual carbon” goals. This paper leverages the phased rollout of UHV projects as a quasi-natural experiment and employs a staggered difference-in-differences model to analyze prefecture-level carbon emissions (2004–2021). Results show UHV operation significantly reduces adjacent areas' emissions, with sustained and robust policy impacts. The effect is stronger in eastern/western regions and growing/mature cities, where energy allocation efficiency improves. Mechanism analysis reveals energy substitution and economies of scale as key drivers. The findings strengthen the empirical link between cross-regional energy allocation and environmental outcomes, offering policy insights for building a modern energy system and achieving synergistic pollution-carbon reduction.