Optimizing Urban Accessibility: Building a 15-Minute City with Steiner Tree Approximation

A Research Paper by Prishaa Shrimali (USA, Grade 10)

Introduction

Urban planning is increasingly focused on creating sustainable, accessible cities where essential services are within easy reach. The 15-minute city (15-MC) model is an innovative approach aimed at structuring urban spaces so that residents can access key services, like healthcare, shopping, and recreational facilities, within a short walking or biking distance. In the study Optimizing Urban Accessibility: Constructing a 15-Minute City Using Steiner Tree Approximation, researchers introduce a method of applying graph theory—particularly the Steiner tree problem—to efficiently design 15-minute cities.

Methodology

The study employs the Steiner tree problem, which seeks to find the minimum-weight network that connects selected key points, called terminals (e.g., service locations). Using this graph-based approach, the model minimizes travel time between key amenities by optimizing the pathways that connect them. Unlike models that place a focus on residential areas, this approach prioritizes service locations, making it computationally efficient.

The model is applied to Manhattan, using the city's pedestrian network to highlight service accessibility. Here, amenities such as pharmacies, post offices, and supermarkets serve as the Steiner tree's focal points. The OSMnx Python library is used to pull data from Open Street Maps, allowing for a practical analysis of service accessibility within a 15-minute walking radius.

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Key Highlights

1. Efficient Service Connectivity: By focusing on connecting service points, this model minimizes computational complexity and offers a feasible layout for urban planners to improve walkability.
2. Dense Network Coverage in Manhattan: The analysis reveals that central and southern Manhattan already supports a high level of walkability, with the Steiner tree model indicating most residents in these areas can reach essential services within a short walk.
3. Areas for Improvement: The study highlights gaps in the northern parts of Manhattan, suggesting areas where pedestrian access to amenities could be enhanced.
4. Digital City Models: The study's approach yields detailed digital models that serve as practical tools for urban planners to optimize mobility, service placement, and sustainable design.

Inference

The Steiner tree-based method for designing a 15-minute city provides urban planners with an actionable framework to improve urban accessibility. While central areas of Manhattan demonstrate a high density of accessible services, regions like northern Manhattan could benefit from increased service points or better connectivity. This graph-based approach also shows promise for future expansions, such as multi-criteria optimization considering factors like environmental impact and cost.

In sum, the paper underscores the effectiveness of leveraging graph theory in urban planning and establishes a solid foundation for implementing sustainable, accessible city models that can adapt to the unique needs of various urban landscapes.