Investigating the impact of a 20mph speed limit intervention on road traffic collisions, casualties, speed and volume in Belfast, UK: 3-year follow-up outcomes of a natural experiment

Hunter, Ruth F., Cleland, Claire L., Busby, John, Nightingale, Glenna, Kee, Frank, Williams, Andrew James, Kelly, Paul, Kelly, Michael P., Milton, Karen ORCID: https://orcid.org/0000-0002-0506-2214, Kokka, Kelly and Jepson, Ruth (2023) Investigating the impact of a 20mph speed limit intervention on road traffic collisions, casualties, speed and volume in Belfast, UK: 3-year follow-up outcomes of a natural experiment. Journal of Epidemiology and Community Health, 77 (1). pp. 17-25. ISSN 0143-005X

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Abstract

Background: Evidence regarding the effectiveness of 20 miles per hour (mph) speed limit interventions is limited, and rarely have long-term outcomes been assessed. We investigate the effect of a 20 mph speed limit intervention on road traffic collisions, casualties, speed and volume at 1 and 3 years post-implementation. Methods: An observational, repeated cross-sectional design was implemented, using routinely collected data for road traffic collisions, casualties, speed and volume. We evaluated difference-in-differences in collisions and casualties (intervention vs control) across three different time series and traffic speed and volume pre-implementation, at 1 and 3 years post-implementation. Results: Small reductions in road traffic collisions were observed at year 1 (3%; p=0.82) and year 3 post-implementation (15%; p=0.31) at the intervention site. Difference-in-differences analyses showed no statistically significant differences between the intervention and control sites over time for road traffic collisions. There were 16% (p=0.18) and 22% (p=0.06) reductions in casualty rates at years 1 and 3 post-implementation, respectively, at the intervention site. Results showed little change in mean traffic speed at year 1 (0.2 mph, 95% CI −0.3 to 2.4, p=0.14) and year 3 post-implementation (0.8, 95% CI −1.5 to 2.5, p=0.17). For traffic volume, a decrease in 57 vehicles per week was observed at year 1 (95% CI –162 to −14, p<0.00) and 71 vehicles at year 3 (95% CI −213 to 1, p=0.05) post-implementation. Conclusion: A 20 mph speed limit intervention implemented at city centre scale had little impact on long-term outcomes including road traffic collisions, casualties and speed, except for a reduction in traffic volume. Policymakers considering implementing 20 mph speed limit interventions should consider the fidelity, context and scale of implementation.

Item Type: Article
Uncontrolled Keywords: epidemiology,prevention,public health,epidemiology,public health, environmental and occupational health ,/dk/atira/pure/subjectarea/asjc/2700/2713
Faculty \ School: Faculty of Medicine and Health Sciences > Norwich Medical School
UEA Research Groups: Faculty of Medicine and Health Sciences > Research Centres > Lifespan Health
Faculty of Medicine and Health Sciences > Research Centres > Population Health
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Depositing User: LivePure Connector
Date Deposited: 30 Jan 2023 10:30
Last Modified: 03 Jan 2024 03:13
URI: https://ueaeprints.uea.ac.uk/id/eprint/90856
DOI: 10.1136/jech-2022-219729

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