The Effects of Compact Urban Form: A qualitative and quantitative evidence review

Cities around the world vary in form, which greatly affects their performance in economic, social, and environmental terms. In most developed nations, compact urban form is being promoted and density and accessibility are seen to generate urban externalities that align with sustainability goals. This working paper by Gabriel Ahlfedlt and Elisabetta Pietrostefani analyses over 300 journal articles in an attempt to: (a) evaluate the evidence; and (b) better understand how compactness impacts, through costs and benefits, upon economic, social and environmental dimensions of urban life. Through rigorous analysis it concludes that pursuit of compact urban forms is beneficial for cities to achieve greater “economic competitiveness and dynamism” and reduce climate change risks. But housing and transport policies need careful attention so that they “accentuate the good parts of compact urban form while minimising the downsides” (page 4).

“The Effects of Compact Urban Form” is prepared for the Coalition for Urban Transitions – a major initiative supporting decision makers to improve the performance of their cities, including reducing climate change risks. It stems from a need for cities to develop policy interventions that redress the negative impacts of compactness, meanwhile retaining the benefits to deliver “healthier and greener cities” (page 3). It is important to note, however, that a significant proportion of its literature base presents empirical experience from the US and Europe. And while there is little disagreement that the benefits of compact urban form outweigh the costs in developed nations, there is significant debate about compactness and density in developing nations, where higher density intensifies health risks associated with poor or lacking infrastructure and housing (pages 5 and 16).

This 32-page working paper has five sections: 1) An introduction, 2) Theoretical Literature, 3) Qualitative results, 4) Quantitative Results on Economic Density, and 5) Conclusion.

Section 2 presents a systematic overview of the theoretical compact city literature and condenses evidence found in the literature, so that the effects of different compact city characteristics can be compared against the same outcome (page 5). In short, it identifies three key compact city characteristics: economic density, morphological density, and mixed land use; and 15 compact city outcome dimensions (page 8). These create 45 potential cause–effect relations.

Section 3 focuses on the qualitative results of the literature analysis. This assesses outcome dimensions and compact city characteristics against 321 collected analyses (page 14). In tabular format, Ahlfedlt and Pietrostefani assign numeric values to the qualitative results and obtain scores according to outcome dimension. They also compare empirical results with expectations in the theoretical literature. To close, they focus on two types of results: a) those relating to the social and environmental outcome categories – safety, pollution reduction, energy efficiency, and health; and b) those relating to country income – in other words a focus on compact city characteristics in low- and middle-income countries.

Section 4 moves onto quantitative results and concentrates on a sub-sample of the analyses regarding economic density. It uses elasticity as a means to compare different studies and provide a unique “comparison of density effects across outcome dimensions” (page 26). Elasticities they use include wage, rent, local public spending and energy use reduction, among others. After modelling the effects of a 10 per cent increase in economic density against outcome dimension-specific results, the authors assess if, and by how much, density benefits outweigh the costs (see Table 9). They conclude that density can further inequality because it benefits homeowners but has negative effects upon rents and first-time buyers.

Section 5 concludes the study and affirms that the empirical evidence supports theoretical implications. In other words, positive effects of compact urban form outweigh negatives effects for urban life (page 31). However, open space preservation, pollution, health, and income inequality are dimensions that currently have more negative effects and specifically need more attention for positive policy intervention.

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Book note prepared by Hannah Keren Lee