Compact 15-minute cities are greener

The 15-minute city concept, which advocates for cities where essential services are accessible within a 15-minute walk or bike ride, has gained significant attention in recent years. However, despite being celebrated for promoting sustainability, large-scale empirical evaluations of the effectiveness of the 15-minute concept in reducing emissions are lacking. To address this gap, we investigate whether cities with better walking accessibility, like 15-minute cities, are associated with lower transportation emissions. Comparing 664 cities worldwide, we find that cities with better walking accessibility to services emit less CO$_2$ per capita for transport. Moreover, we observe that among cities with similar average accessibility, those that span larger areas tend to emit more. Our findings highlight the effectiveness of decentralised urban planning, especially the proximity-based 15-minute city, in promoting sustainable mobility. However, they also emphasise the need to integrate local accessibility with urban compactness and efficient public transit, which are vital in large cities.