Bicycle infrastructure and the incidence rate of crashes with cars: A case-control study with Strava data in Atlanta

Michael D Garber; Kari E Watkins; W Dana Flanders; Michael R Kramer; R L Felipe Lobelo; Stephen J Mooney; David J Ederer; Lauren E McCullough

doi:10.1016/j.jth.2023.101669

Bicycle infrastructure and the incidence rate of crashes with cars: A case-control study with Strava data in Atlanta

J Transp Health. 2023 Sep:32:101669. doi: 10.1016/j.jth.2023.101669. Epub 2023 Aug 11.

Authors

Michael D Garber^{1

2

3}, Kari E Watkins⁴, W Dana Flanders^{1

5}, Michael R Kramer¹, R L Felipe Lobelo⁶, Stephen J Mooney^{7

8}, David J Ederer⁹, Lauren E McCullough¹

Affiliations

¹ Department of Epidemiology, Rollins School of Public Health, Emory University, Atlanta, GA, USA.
² Department of Environmental and Radiological Health Sciences, Colorado State University, Fort Collins, CO, USA.
³ Herbert Wertheim School of Public Health and Human Longevity Science & Scripps Institution of Oceanography, UC San Diego, San Diego, CA, USA.
⁴ Civil and Environmental Engineering, University of California, Davis, Davis, CA, USA.
⁵ Department of Biostatistics and Bioinformatics, Rollins School of Public Health, Emory University, Atlanta, GA, USA.
⁶ Hubert Department of Global Health, Rollins School of Public Health, Emory University, Atlanta, GA, USA.
⁷ Department of Epidemiology, University of Washington School of Public Health, USA.
⁸ Harborview Injury Prevention & Research Center, University of Washington, Seattle, WA, USA.
⁹ Civil and Environmental Engineering, Georgia Institute of Technology, Atlanta, GA, USA.

PMID: 38196814
PMCID: PMC10773466 (available on 2024-09-01)
DOI: 10.1016/j.jth.2023.101669

Abstract

Introduction: Bicycling has individual and collective health benefits. Safety concerns are a deterrent to bicycling. Incomplete data on bicycling volumes has limited epidemiologic research investigating safety impacts of bicycle infrastructure, such as protected bike lanes.

Methods: In this case-control study, set in Atlanta, Georgia, USA between 2016-10-01 and 2018-08-31, we estimated the incidence rate of police-reported crashes between bicyclists and motor vehicles (n = 124) on several types of infrastructure (off-street paved trails, protected bike lanes, buffered bike lanes, conventional bike lanes, and sharrows) per distance ridden and per intersection entered. To estimate underlying bicycling (the control series), we used a sample of high-resolution bicycling data from Strava, an app, combined with data from 15 on-the-ground bicycle counters to adjust for possible selection bias in the Strava data. We used model-based standardization to estimate effects of treatment on the treated.

Results: After adjustment for selection bias and confounding, estimated ratio effects on segments (excluding intersections) with protected bike lanes (incidence rate ratio [IRR] = 0.5 [95% confidence interval: 0.0, 2.5]) and buffered bike lanes (IRR = 0 [0,0]) were below 1, but were above 1 on conventional bike lanes (IRR = 2.8 [1.2, 6.0]) and near null on sharrows (IRR = 1.1 [0.2, 2.9]). Per intersection entry, estimated ratio effects were above 1 for entries originating from protected bike lanes (incidence proportion ratio [IPR] = 3.0 [0.0, 10.8]), buffered bike lanes (IPR = 16.2 [0.0, 53.1]), and conventional bike lanes (IPR = 3.2 [1.8, 6.0]), and were near 1 and below 1, respectively, for those originating from sharrows (IPR = 0.9 [0.2, 2.1]) and off-street paved trails (IPR = 0.7 [0.0, 2.9]).

Conclusions: Protected bike lanes and buffered bike lanes had estimated protective effects on segments between intersections but estimated harmful effects at intersections. Conventional bike lanes had estimated harmful effects along segments and at intersections.

Keywords: Atlanta; Bicycle infrastructure; Bicycling safety; Case-control studies; Causal inference; Georgia; Strava.

Grants and funding

F31 HL143900/HL/NHLBI NIH HHS/United States