CHAPTER 1

Introduction

The NHTSA reports that 966 bicyclists were killed in traffic crashes in 2021, while average annual bicyclist fatalities have risen from 670 per year (2007-2011) to 779 (2012 to 2016) to 890 (2017 to 2021). In response to these trends (and similar trends for pedestrians), states and municipalities across the U.S. are increasingly adopting Vision Zero, Towards Zero Deaths, and/or similar goals and related plans in an effort to improve bicycling safety and reduce the disproportionate proportion of road deaths for cyclists. Critical to a successful effort to improve cycling safety is an understanding of the dynamics that lead to fatal and severe cyclist crashes. NHTSA reports that 70% of cyclist fatalities from 2008-2017 occurred in urban areas, and 31% occurred at intersections (NHTSA, 2010-2019). Data for non-fatal injuries are less readily available at a large scale, but studies that use sample estimates (e.g., National Automotive Sampling System General Estimates System (NASS GES)), as well as state and local crash databases, indicate intersections are routinely the site of bicycle crashes and injuries. To reduce bicyclists’ injuries and fatalities, it is necessary to implement solutions that can improve intersection cycling safety (NTSB, 2019; Thomas et al., 2019).

Communities throughout the United States are adopting policies and practices to improve safety for bicyclists. Planners, engineers, and designers who are implementing bikeways struggle with decisions selecting bikeway treatments at intersections given the lack of information in published design guidance. These practitioners need a better understanding of the safety performance of design treatments in different contexts to inform design decisions. Better information on actual safety outcomes of designs can be combined with the body of knowledge about perceived safety or comfort to provide improved guidance about preferred treatments at intersections.

Research Objective and Project Process

The objective of this research, NCHRP 15-73 Design Options to Reduce Turning Motor Vehicle-Bicycle Conflicts, is to develop guidelines and tools to provide practitioners a better understanding of the safety performance of design treatments to use to reduce turning conflicts between motor vehicles and bicycles at controlled intersections.

The research was framed by a state of the practice review that included the existing literature, a summary of current design guidance, and a practitioner interview process. A macro-level crash analysis examined bicycle crashes and injuries at a broad scale (e.g., using multiple state databases) to contribute to a thorough understanding of bicycle crashes at intersections, including type, frequency, and severity, in varying land use contexts (urban, suburban, rural) and was used to provide additional context to the research design Three research approaches were used to explore the safety performance of intersection treatment types for bicycles at intersections. Figure 1 provides a visual depiction of how the different analyses relate to each other, an overview of the primary questions, and the scale of the approach. Each method is robust and produced valuable information, however, the differing scale, focus and limitations of each approach means that synthesizing the results requires interpretations and judgement.

• Micro-level crash analysis examines total bicycle crashes on the intersection approach, injuries, roadway design, operational variables, and related risk (e.g., accounting for exposure) at a smaller scale (e.g., at 150-250 intersection sites) to clarify how exposure and various roadway design factors influence risk across a variety of facility types and site-specific contexts.
• Video-based surrogate safety analysis examines left- and right-turn conflicts (though most of the observed conflicts where right-turn conflicts) via surrogate safety measures at a further targeted scale to provide additional insight into the dynamics between bicycle safety and known risk factors like turning volumes, speed, and design features.
• Human factors study explores and validates some design assumptions about interactions between right-turn vehicles and bicycles, reaction times, cognitive behaviors, and mechanisms of a driving/bicycle simulator, and possibly considers novel designs not currently constructed in the U.S.

Finally, the decision tool was designed to provide information on relative safety performance and inform design-related thresholds and guidelines. Figure 1 shows the flow chart of the research methods and how they were used to provide guidelines for practitioners through the decision tool.

Report Organization

This report is organized into ten chapters. The following chapters are:

• Chapter 1: Introduction provides an overview and lays out the objectives of the research.

Section 1: State of the Practice

• Chapter 2: Literature Review includes review of published literature related to turning conflicts between motor vehicles and bicycles at controlled intersections.
• Chapter 3: Summary of Design Guidance summarizes current design guidance available in the United States focusing on implementing bikeway treatments at intersections.
• Chapter 4: Practitioner Interviews includes the findings from semi-structured interviews with practitioners at 16 agencies, exploring how practitioners are making design decisions today, typical challenges they encounter, and what additional research would help their future decision-making and design processes.

Section 2: Research Methods and Findings

• Chapter 5: Overview of Research Methods and Site Selection describes the process used to identify and collect data elements on 853 possible sites (intersection approaches) for analysis and to refine the list of sites to 561 sites for the micro crash analysis and video-based conflict analysis.
• Chapter 6: Crash Analysis summarizes the macro-crash analysis and then describes the detailed micro crash analysis of 851 intersection approaches using bivariate descriptive and multivariate statistical analysis to examine factors associated with bicyclist-motorist crashes at each intersection approach in four case cities.
• Chapter 7: Video-Based Conflict Analysis presents the conflict analysis derived from automated video analysis of 2,187 hours of video at 28 locations with the five treatment types selected in four cities – Austin, Minneapolis, New York City and Seattle.
• Chapter 8: Human Factors Study for Selected Sites presents the results of an experiment assessing driver visual attention to bicyclists and travel speed in a simulated/virtual environment. A sample of 40 drivers made 640 right-turns at the design intersections.
• Chapter 9: Synthesis and Summary of Results combines key findings from each of the analysis approaches and recommends future research.

Section 3: Development of Practice-Related Tools

• Chapter 10: Decision Tool and Guidelines Summary, Implementation and Training explains the process for developing the Decision Tool and Design Guidelines, and training materials.