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Integrating complex systems science into road safety research and practice, Part 2: applying systems tools to the problem of increasing pedestrian death rates
  1. Rebecca B Naumann1,
  2. Jill Kuhlberg2,
  3. Laura Sandt3,
  4. Stephen Heiny3,
  5. Wesley Kumfer3,
  6. Stephen W Marshall1,
  7. Kristen Hassmiller Lich2
  1. 1 Epidemiology Department and Injury Prevention Research Center, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA
  2. 2 Health Policy and Management Department, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA
  3. 3 University of North Carolina Highway Safety Research Center, Chapel Hill, North Carolina, USA
  1. Correspondence to Dr Rebecca B Naumann, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA; rnaumann{at}


Objectives To provide a specific example of how systems dynamics tools can increase understanding of stakeholder ‘mental models’ and generate robust systems-based hypotheses about the escalating problem of rising pedestrian death rates in the USA.

Methods We designed and facilitated two group model building (GMB) workshops. Participants generated causal loop diagrams (CLDs) individually and in small groups to explore hypotheses concerning time–dynamic interacting factors underlying the increasing rates of pedestrian deaths. Using a grounded theory approach, research team members synthesised the structures and hypotheses into a single CLD.

Results CLDs from the 41 participants indicated four core factors hypothesised to have a direct impact on pedestrian fatalities: pedestrian–vehicle crashes, vehicle speed at the time of the crash, vehicle size/dimensions and emergency response time. Participants diagrammed how actions and reactions impacted these proximal factors over time and led to ripple effects throughout a larger system to generate an increase in pedestrian deaths. Hypothesised contributing mechanisms fell within the following broad categories: community responses; research, policy and industry influence; potential unintended consequences of responses to pedestrian deaths; and the role of sprawl.

Conclusions This application of systems science tools suggested several strategies for advancing injury prevention research and practice. The project generated robust hypotheses and advanced stakeholder communication and depth of understanding and engagement in this key issue. The CLD and GMB process detailed in this study provides a concrete example of how systems tools can be adopted and applied to a transportation safety topic.

  • systems science
  • injury prevention
  • road safety
  • system dynamics
  • pedestrian

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  • Contributors All the authors contributed to the study design and writing of this manuscript and have approved the final manuscript. RBN and JK conducted all the analyses.

  • Funding This project was supported by the Collaborative Sciences Center for Road Safety (, a United States Department of Transportation National University Transportation Center (award # 69A3551747113). The UNC Injury Prevention Research Center is supported by an award (R49/CE0042479) from the Centers for Disease Control and Prevention.

  • Competing interests No, there are no competing interests for any author.

  • Patient consent for publication Not required.

  • Ethics approval The University of North Carolina at Chapel Hill’s Institutional Review Board reviewed and approved this research.

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

  • Data availability statement All data relevant to the study are included in the article or uploaded as supplementary information.