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

Disi Tian; Susan G Gerberich; Hyun Kim; Andrew D Ryan; Darin J Erickson; Nichole L Morris

doi:10.1136/injuryprev-2021-044321

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

Inj Prev. 2022 Jun;28(3):204-210. doi: 10.1136/injuryprev-2021-044321. Epub 2021 Oct 29.

Authors

Disi Tian¹, Susan G Gerberich², Hyun Kim², Andrew D Ryan², Darin J Erickson³, Nichole L Morris⁴

Affiliations

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 tianx229@umn.edu.
² 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.
³ Division of Epidemiology and Community Health, School of Public Health, University of Minnesota, Minneapolis, Minnesota, USA.
⁴ HumanFIRST Laboratory, Department of Mechanical Engineering, University of Minnesota, Minneapolis, Minnesota, USA.

PMID: 34716178
DOI: 10.1136/injuryprev-2021-044321

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.

Keywords: engineering; epidemiology; motor vehicle � occupant; multiple injury; rural.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Accidents, Traffic* / prevention & control
Humans
Research Design
Rural Population*