This paper investigates the causal impact of city shape on car use and emissions within French metropolitan areas. We in particular analyze the influence of a novel indicator of urban geometry that captures differences in the built environment likely to nurture or alleviate car dependence. Individual data allow us to separate the effects of urban geometry and households' spatial sorting, while historical and geological instruments help tackling ‘endogeneous density’ issues. Cities with a more compact, fractal and diverse spatial layout have lower car emissions per household. Urban geometry drives a bell-shaped relationship between city size and the ‘carprint’ of households: small cities compensate for their lack of Density or Diversity by an environmentally-friendly geometric Design, whereas medium cities exhibit heavier driving footprints.

本文研究了城市形态对法国大都市区内汽车使用和排放的因果影响。我们特别分析了一个新的城市几何指标的影响，该指标捕捉了可能培养或减轻汽车依赖的建筑环境的差异。个人数据使我们能够将城市几何和家庭空间分类的影响分开，而历史和地质仪器有助于解决“内生密度”问题。空间布局更紧凑、分形和多样化的城市，每户家庭的汽车排放量更低。城市几何在城市规模和家庭的“车印”之间形成钟形关系：小城市通过环保的几何设计来弥补密度或多样性的不足，而中等城市则表现出更重的驾驶足迹。