The Impact of Parking Policies on the Long-Term Vitality of American Cities

Garrick, Norman; Atkinson-Palombo, Carol · 2015 · ROSA P / New England University Transportation Center

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Summary

This study investigates the causal relationship between citywide parking supply and automobile use, challenging the prevailing "predict-and-provide" approach used in urban planning. Most U.S. municipalities enforce minimum parking requirements based on estimated demand, a practice that increases construction costs, consumes land, and potentially encourages driving. While prior research indicates a correlation between parking supply and vehicle usage, it has not definitively established whether increased parking causes higher automobile use or merely responds to it. This research aims to resolve this causality question to inform long-term transportation policies. Due to the lack of comprehensive historical travel surveys and reliable databases of past parking supplies, the authors could not employ standard statistical modeling or controlled experiments. Instead, they developed original estimates of parking provision for nine U.S. cities for the years 1960, 1980, and 2000, using aerial photographs. They paired this data with journey-to-work survey data from the U.S. Census Bureau. To infer causality, the study applied the Bradford Hill criteria, a framework adopted from epidemiology that evaluates associations based on factors such as strength, consistency, and biological plausibility. The analysis revealed that an increase in parking provision from 0.1 to 0.5 spaces per resident and employee was associated with a roughly 30 percentage point increase in the commuter automobile mode share. The authors demonstrated that the available data satisfied a majority of the Bradford Hill criteria, with no evidence conflicting with the hypothesis. Consequently, they inferred that increased parking provision is a likely cause of increased driving among residents and employees. These findings suggest that parking generates induced demand, undermining the justification for minimum parking requirements in urban areas. The study concludes that planners should move away from policies that aim to meet theoretical demand and instead adopt mechanisms such as maximum parking allowances and appropriate pricing to manage supply. By recognizing the causal link between parking availability and automobile use, cities can better achieve long-term transportation goals, including reduced congestion, pollution, and traffic fatalities.

Key finding

An increase in parking provision from 0.1 to 0.5 spaces per resident and employee is associated with a roughly 30 percentage point increase in commuter automobile mode share.

Methodology

dataset

Sample size: 9

Provenance

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Summary generated by qwen3.6-27b-prismaquant on 2026-06-10; verification: verified.

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• urban rural setting