Urban design has never been more important — and more difficult. Our cities have grown larger and more complex and along the way, they’ve started accentuating inequalities rather than reducing them. However, one innovative solution, called the “15-minute city” promises to be a game changer for cities.

A 15-minute city is an urban design concept where essential services and amenities — such as schools, healthcare, groceries, parks, and public spaces — are accessible within a 15-minute walk or bike ride from any resident’s home. The idea promotes sustainability by reducing the need for cars, cutting down on carbon emissions, and fostering stronger local communities. It aims to create self-sufficient neighborhoods that prioritize proximity and enhance the quality of life through improved accessibility and reduced commuting times.

This approach promises to transform sprawling metropolises into vibrant, accessible hubs. In these cities essential services and amenities are within a short walk or bike ride from people’s homes. But can this actually work? New research led by Matteo Bruno and his colleagues says it can, but we need to consider the different urban contexts around the world.

Everything should be close to you

The main idea is that you should have essential services (and things you commonly use) very close to you. Schools, healthcare, grocery stores, and parks should all be available within 15 minutes of your home. And that’s when walking or cycling, not driving.

If you have everything close to you, that means you don’t need to drive as much. The roads are emptier and cleaner, there’s less pollution; and the community has stronger ties and local involvement. This isn’t exactly a new idea but the model gained significant attention during the COVID-19 pandemic. Lockdowns highlighted the importance of local neighborhoods and reduced the need for long commutes.

Some cities, particularly in Europe, are already embracing this idea. Most famously, Milan, Paris, and Barcelona have pledged to truly become 15-minute cities and the new research shows the progress is real.

The researchers used a new metric, proximity time (PT), to measure how long it takes residents in different parts of a city to access these services. Cities were then compared based on the fraction of their population living within 15 minutes of essential services, a quantity the researchers called F15.

In several European cities, a large portion of the population already benefits from high levels of accessibility. In contrast, car-centric cities (especially US cities like Atlanta and Dallas) exhibited significant accessibility gaps.

The study also highlighted inequalities within the cities themselves. Often, urban centers are well-served, while peripheral areas are left with few options, exacerbating social and economic disparities. When the team compared their results with the inequality index (the Gini coefficient) they found a very good fit. Cities that were closer to becoming 15-minute cities were more equal, while those with gaps in accessibility also tended to have greater inequality.

Describing cities algorithmically

The problem is that it’s hard to quantify how close a city is to being a 15-minute city. In their analysis of approximately 10,000 cities, Bruno and colleagues found considerable variation. So, they classified “essential services” into 9 categories: outdoor activities, learning, supplies, eating, moving, cultural activities, physical exercise, services, and healthcare.

One of the most innovative aspects of the study is the development of an algorithm. This was designed to optimize the distribution of services within a city. Instead of creating new infrastructure from scratch, the algorithm focuses on redistributing existing points of interest (POIs), such as schools, healthcare centers, and stores, to better serve the population.

The algorithm takes into account the city’s population density and the current location of services to determine where resources should be reallocated. By relocating services to underserved areas, cities could significantly improve the number of residents living in a 15-minute city condition without depriving well-served areas.

For example, in cities like Atlanta, where services are concentrated in a few central areas, the algorithm suggested that over 70% of existing POIs would need to be relocated to achieve more balanced accessibility. In contrast, cities like Zurich or Lisbon, which already have a more equitable distribution of services, required minimal redistribution.

This approach also highlights one of the most important aspects of this concept: that not all cities can become 15-minute cities; or at least, not in the current approach.

Geography is key

One of the key findings of the study is that the 15-minute model is not universally applicable, particularly in low-density urban areas. Cities with sprawling suburban landscapes, face significant challenges in implementing this model due to their reliance on cars and large distances between residential areas and services.

In such cities, even with the algorithmic redistribution of services, achieving widespread 15-minute accessibility is difficult. This study suggests that the 15-minute city model needs to be adapted or supplemented with other strategies in sprawling urban areas. The study proposes that cities with low population densities may need to rely more heavily on public transportation and other mobility solutions to connect residents with essential services. In other words, the 15-minute city should also include public transit.

The study doesn’t dismiss the model but instead suggests a more nuanced approach. Bruno and colleagues argue that the proximity-based paradigm needs to take into account local population densities and urban layouts. Instead of focusing solely on time-based accessibility, cities should consider value-based accessibility, where the quality and availability of services are tailored to the needs of local populations.

For example, not every neighborhood needs to have the full range of services within a 15-minute radius. However, there should be enough essential services, such as healthcare and education, to meet basic needs. Non-essential services, such as entertainment venues or specialized medical facilities, could be located further away but connected by efficient public transportation.

The journey towards truly inclusive 15-minute cities is just beginning, and the path ahead will require collaboration, innovation, and a deep commitment to social equity. But with the right tools and strategies, cities around the world can become vibrant, sustainable spaces where everyone has the opportunity to thrive.

The study was published in Nature Cities. https://doi.org/10.1038/s44284-024-00119-4