The whole "15-minute city" dream where everything is a short walk away is actually mathematically impossible for most big cities.
arXiv · March 13, 2026 · 2603.12122
Why it matters
Urban planners want everyone to live within a 15-minute walk of their job, but this study shows that the natural distribution of business sizes and locations creates a 'hard limit' on short commutes. For a city like Paris, no amount of rezoning can fix the commute times without a total, forced restructuring of the entire economy.
From the abstract
The `15-minute city' has emerged as a central paradigm in urban planning, promoting universal access to work and essential services within short travel times. Its feasibility-particularly for commuting to work-has however rarely been examined quantitatively. Here, we show that proximity to employment is fundamentally constrained by the internal structure of urban economies. Combining urban geometry with empirically observed firm-size distributions, we derive a lower bound on commuting times that