The built environment

Proposed and experimental methods

Methods that are proposed, under trial, approved in some places, or tried and then failed. Each shows a stage label and an evidence rating. A stage label shows how far a method has progressed, not whether it works. The stage labels are explained on the environmental factor page.

• Greening and cleaning vacant lots (Large trial, B). In a citywide cluster randomized trial of 541 vacant lots in Philadelphia, restoring lots (clearing trash, planting grass and some trees, adding a low fence, and monthly upkeep) was followed in neighborhoods below the poverty line by 29.1% less gun violence, 13.3% less crime overall, and 21.9% fewer burglaries, and nearby residents reported 57.8% fewer safety concerns about going outside (Branas et al., 2018). A separate analysis of shootings found reductions of 6.8% for greening and 9.2% for cheaper mowing and trash cleanup, with no sign that shootings moved to nearby areas (Moyer et al., 2019). Among 342 residents with follow-up data, those near greened lots reported feeling depressed 41.5% less and worthless 50.9% less, while the 62.8% drop in overall poor mental health was not significant (South et al., 2018). All results come from one city and one research group.
• Upzoning, allowing denser housing (Approved but not scaled, contested, C). Auckland upzoned about three quarters of its residential land in 2016, and a quasi-experimental study found strong evidence that construction increased, even after allowing for building that would have happened elsewhere (Greenaway-McGrevy and Phillips, 2023). A reanalysis published on an economics newsletter, not peer reviewed, argued that the result depends on leaving out consents in Special Housing Areas and on assuming linear pre-reform trends, and that with those changes the estimate shrinks or turns negative (Fresh Economic Thinking, n.d.). In Minneapolis, which ended single-family-only zoning and made other land use reforms, the housing stock grew 12% from 2017 to 2022 while rents rose 1% versus 14% in the rest of Minnesota, a comparison without controls for other factors (Liang et al., 2024).
• Low traffic neighborhoods (Approved but not scaled, contested, B). Builds on superblocks (see "Chronic disease, obesity, and physical inactivity" in the biological factors). Low traffic neighborhoods use barriers or cameras to stop through traffic on residential streets. Of 113 introduced across London between 2015 and 2024, 27 were later removed, and their introduction was associated with 35% fewer road injuries and 37% fewer people killed or seriously injured inside them, with no overall change on boundary roads and injuries returning to previous levels where schemes were removed (Furlong et al., 2025). In interviews, some disabled residents reported longer journeys and access problems, and many residents of boundary roads perceived more traffic and pollution (Larrington-Spencer et al., 2026).
• Neighborhood tree planting as a health trial (Early trial, C). The Green Heart Project in Louisville, Kentucky, matched 8 pairs of target and control areas, examined 735 residents before planting, and in 2022 planted more than 8,000 mature, mostly evergreen trees and shrubs in the target areas to test effects on air pollution and cardiovascular health (Bhatnagar et al., 2026). Health results after planting have not yet been reported.
• The 15-minute city (Theoretical, C). Proposed by Carlos Moreno in 2016, the idea is to organize cities so that daily needs are within a short walk or bike ride, framed as "chrono-urbanism" (Moreno et al., 2021). The founding paper is a perspective article, and no outcome trial of the full concept was found.

Sources cited on this page

1. Park, R. J., Goodman, J., Hurwitz, M., & Smith, J. (2020). Heat and learning. American Economic Journal: Economic Policy, 12(2), 306-339. AEA A Strong
2. Engemann, K., et al. (2019). Residential green space in childhood is associated with lower risk of psychiatric disorders. PNAS, 116(11), 5188-5193. DOI C Limited
3. Bhatnagar, A., Keith, R., Yeager, R., Riggs, D., Sears, C., Bucknum, B., et al. (2026). The Green Heart Project: Objectives, design, and methods. American Journal of Epidemiology, 195(5), 1416-1428. link C Limited
4. Branas, C. C., South, E., Kondo, M. C., Hohl, B. C., Bourgois, P., Wiebe, D. J., et al. (2018). Citywide cluster randomized trial to restore blighted vacant land and its effects on violence, crime, and fear. Proceedings of the National Academy of Sciences, 115(12), 2946-2951. link B Moderate
5. Furlong, J., Fevyer, D., Armstrong, B., Edwards, P., Aldred, R., & Goodman, A. (2025). Low Traffic Neighbourhoods in London reduce road traffic injuries: A controlled before-and-after analysis (2012-2024). Injury Prevention. Advance online publication. link B Moderate
6. Greenaway-McGrevy, R., & Phillips, P. C. B. (2023). The impact of upzoning on housing construction in Auckland. Journal of Urban Economics, 136, 103555. link C Limited: (changed from B on October 8, 2026, because of an unresolved critique affecting the size of the effect)
7. Larrington-Spencer, H. M., Verlinghieri, E., Aldred, R., Lawlor, E., & Furlong, J. (2026). Resident experience of new Low Traffic Neighbourhoods in London: Qualitative insights from a mixed methods study. Public Health Research, 14(21), 1-32. link C Limited
8. Liang, L., Staveski, A., & Horowitz, A. (2024, January 4). Minneapolis land use reforms offer a blueprint for housing affordability. Pew. link C Limited
9. Moreno, C., Allam, Z., Chabaud, D., Gall, C., & Pratlong, F. (2021). Introducing the "15-Minute City": Sustainability, resilience and place identity in future post-pandemic cities. Smart Cities, 4(1), 93-111. link C Limited
10. Moyer, R., MacDonald, J. M., Ridgeway, G., & Branas, C. C. (2019). Effect of remediating blighted vacant land on shootings: A citywide cluster randomized trial. American Journal of Public Health, 109(1), 140-144. link B Moderate
11. South, E. C., Hohl, B. C., Kondo, M. C., MacDonald, J. M., & Branas, C. C. (2018). Effect of greening vacant land on mental health of community-dwelling adults: A cluster randomized trial. JAMA Network Open, 1(3), e180298. link B Moderate

Every source for this factor is listed on the environmental factor page.