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Evaluation of the efficacy of an intersection conflict warning system at two-way stop-controlled rural intersections: difference-in-differences and triple-difference analytical approaches
  1. Disi Tian1,
  2. Susan G Gerberich1,
  3. Hyun Kim1,
  4. Andrew D Ryan1,
  5. Darin J Erickson2,
  6. Nichole L Morris3
  1. 1 Midwest Center for Occupational Health and Safety Education and Research Center, Division of Environmental Health Sciences, School of Public Health, University of Minnesota, Minneapolis, Minnesota, USA
  2. 2 Division of Epidemiology and Community Health, School of Public Health, University of Minnesota, Minneapolis, Minnesota, USA
  3. 3 HumanFIRST Laboratory, Department of Mechanical Engineering, University of Minnesota, Minneapolis, Minnesota, USA
  1. Correspondence to Dr Disi Tian, Midwest Center for Occupational Health and Safety Education and Research Center, Division of Environmental Health Sciences, School of Public Health, University of Minnesota, Minneapolis, MN 55455, USA; tianx229{at}umn.edu

Abstract

Objective Intersection conflict warning systems (ICWSs) have been implemented at high-risk two-way stop-controlled intersections to prevent right-angle crashes and associated injuries. This study involved investigation of the impacts of ICWSs on crash reductions.

Methods The study used a quasi-experimental design to analyse the potential causal relations between Minnesota’s ICWSs and various crash rate outcomes (including total, injury, non-injury, targeted right-angle and non-right-angle crashes) in pre-post analyses. A restricted randomisation method enabled identification of three controls to each ICWS treatment intersection, and included as many comparable intersection characteristics as possible. Annual crash rates (per year per intersection) were analysed over the same periods before and after system activation for treatment and control intersections in each matched group. Pre-crash data for 3 years and post-crash data for up to 5 years were included, ranging from 2010 to 2018. Negative binomial regression models with generalised estimating equations were applied to estimate the average, immediate and continuing treatment effects of ICWSs, through the difference-in-differences and difference-in-difference-in-difference approaches, respectively.

Results The ICWS treatment was significantly associated with a decreasing trend for targeted right-angle crash rates posttreatment. Although not statistically significant, most crash rate outcomes appeared to be elevated immediately after treatment (statistically significant for sideswipe crashes only). Pre–post differences in average crash rates (over entire periods), except for incapacitating injury-related crashes, were not statistically significant between treatment and control intersections.

Conclusions The study provided important insight into potential causal associations between intersection safety countermeasures and crashes at high-risk rural two-way stop-controlled intersections.

  • multiple injury
  • engineering
  • motor vehicle � occupant
  • epidemiology
  • rural

Data availability statement

Data are available upon reasonable request. Data may be obtained from a third party and are not publicly available.

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Data availability statement

Data are available upon reasonable request. Data may be obtained from a third party and are not publicly available.

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Footnotes

  • Contributors DT, SGG, HK and ADR conceived and designed the study, with SGG having a major advising role. DT, ADR and NLM contributed to the acquisition of data. DT performed data management and data analysis. HK, ADR and DE provided critical feedback to the statistical methodologies. DT, SGG and ADR contributed to the initial draft of the manuscript. All authors reviewed, revised and approved the manuscript.

  • Funding The research was supported, in part, by the Midwest Center for Occupational Health and Safety, Education and Research Center (T42OH008434), Pilot Project Research Fund through National Institute for Occupational Safety and Health, Centers for Disease Control, and Department of Health and Human Services.

  • Competing interests The contents and interpretations of this effort are solely the responsibility of the authors. There is no conflict of interest with the funding agency, Minnesota Department of Transportation, or other associated entities.

  • Patient and public involvement Patients and/or the public were not involved in the design, or conduct, or reporting, or dissemination plans of this research.

  • Provenance and peer review Not commissioned; externally peer reviewed.

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