Walking is the most sustainable form of urban mobility, but is compromised by uncomfortable or unhealthy sun exposure, which is an increasing problem due to global warming. Shade from buildings can provide cooling and protection for pedestrians, but the extent of this potential benefit is unknown. Here we explore the potential for shaded walking, using building footprints and street networks from both synthetic and real cities. We introduce a route choice model with a sun avoidance parameter $\alpha$ and define the CoolWalkability metric to measure opportunities for walking in shade. We derive analytically that on a regular grid with constant building heights, CoolWalkability is independent of $\alpha$, and that the grid provides no CoolWalkability benefit for shade-seeking individuals compared to the shortest path. However, variations in street geometry and building heights create such benefits. We further uncover that the potential for shaded routing differs between grid-like and irregular street networks, forms local clusters, and is sensitive to the mapped network geometry. Our research identifies the limitations and potential of shade for cool, active travel, and is a first step towards a rigorous understanding of shade provision for sustainable mobility in cities.

翻译：步行是城市出行中最可持续的方式，但常因不适或不健康的日晒而受限，而全球变暖正使这一问题日益加剧。建筑物阴影可为行人提供降温和防护，但这一潜在益处的程度尚不明确。本文结合合成城市与真实城市的建筑轮廓及街道路网，探索遮阳步行的潜力。我们引入一个包含避阳参数$\alpha$的路径选择模型，并定义“CoolWalkability”指标以衡量步道遮阳机会的可达性。通过解析推导得出：在建筑高度恒定的规则网格中，CoolWalkability与$\alpha$无关，且对寻求遮阳的行人而言，该网格相较于最短路径并未提供额外的CoolWalkability收益。然而，街道几何形态与建筑高度的变化可创造此类收益。我们进一步揭示，网格状与不规则街道路网中遮阳路径的潜力存在差异，呈现局部聚集特征，且对映射后的路网几何结构敏感。本研究明确了遮阳对凉爽、主动出行的局限性与潜力，为严谨理解城市可持续出行中遮阳供给机制奠定了初步基础。