National Academies Press: OpenBook

Pedestrian and Bicycle Safety Performance Functions (2023)

Chapter: Section 1 - Introduction

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Suggested Citation:"Section 1 - Introduction." National Academies of Sciences, Engineering, and Medicine. 2023. Pedestrian and Bicycle Safety Performance Functions. Washington, DC: The National Academies Press. doi: 10.17226/27294.
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Suggested Citation:"Section 1 - Introduction." National Academies of Sciences, Engineering, and Medicine. 2023. Pedestrian and Bicycle Safety Performance Functions. Washington, DC: The National Academies Press. doi: 10.17226/27294.
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Suggested Citation:"Section 1 - Introduction." National Academies of Sciences, Engineering, and Medicine. 2023. Pedestrian and Bicycle Safety Performance Functions. Washington, DC: The National Academies Press. doi: 10.17226/27294.
×
Page 6
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Suggested Citation:"Section 1 - Introduction." National Academies of Sciences, Engineering, and Medicine. 2023. Pedestrian and Bicycle Safety Performance Functions. Washington, DC: The National Academies Press. doi: 10.17226/27294.
×
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Suggested Citation:"Section 1 - Introduction." National Academies of Sciences, Engineering, and Medicine. 2023. Pedestrian and Bicycle Safety Performance Functions. Washington, DC: The National Academies Press. doi: 10.17226/27294.
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4 1.1 Background In 2010, the American Association of State Highway and Transportation Officials (AASHTO) published the first edition of the Highway Safety Manual (HSM) (AASHTO 2010). This was an important step forward in providing safety analysis tools for transportation agencies. The HSM has become the premier document in the United States for incorporating quantitative safety analysis in the highway transportation project development process. The HSM is divided into four parts: • Part A – Introduction, Human Factors, and Fundamentals • Part B – Roadway Safety Management Process • Part C – Predictive Method • Part D – Crash Modification Factors HSM Part C includes predictive methods that can be used by transportation agencies to anticipate the safety performance of new facilities, assess the safety performance of existing facilities, or estimate the expected effectiveness of proposed improvements to existing facilities. In preparing the first edition of the HSM, choices had to be made based on funding limitations, availability of data, and highway agency priorities concerning which facility types and crash types would be addressed and the level of complexity of the models. Several National Cooperative Highway Research Program (NCHRP) projects have recently been completed, several more are currently ongoing, and more are planned to expand the knowledge and procedures provided in the first edition of the HSM. The HSM Part C provides predictive methods for estimating the expected average crash fre- quency (including by crash severity and collision type) of a network, facility, or individual site. The estimation of crash frequency with the Part C methods uses a combination of safety perfor- mance functions (SPFs), crash modification factors (CMFs), and calibration factors. A decision has been made to rename the HSM Part C CMFs as adjustment factors in the second edition of the HSM (HSM2). Therefore, CMFs that will be used in conjunction with the SPFs developed in this research will be referred to as adjustment factors, or AFs, throughout this report. The crash prediction models in HSM Part C are most suited for estimating expected fre- quencies of multiple- and single-vehicle motor vehicle crashes, excluding pedestrian and bicycle crashes. With the exception of a comprehensive pedestrian safety prediction model for urban and suburban signalized intersections, the models in HSM Part C estimate pedestrian and bicycle safety based on the proportion of pedestrian and bicycle crashes to motor vehicle crashes. This generalized approach for determining site-specific estimates of pedestrian and bicycle crashes is not sensitive to site-specific conditions that influence pedestrian and bicycle crashes (includ- ing exposure and infrastructure) and provides little information for evaluating the site-specific effects of proposed projects intended to improve pedestrian and bicycle safety. S E C T I O N 1 Introduction

Introduction 5   Explicit consideration of pedestrian and bicycle safety, beyond urban and suburban signalized intersections, is critical for the implementation of future editions of the HSM. Pedestrian and bicyclist fatalities have been increasing since about 2010 and now account for approximately 20 percent of all roadway fatalities (NHTSA 2021a). Incorporating more SPFs into future edi- tions of the HSM that explicitly account for site-specific conditions that influence pedestrian and bicycle crashes will provide transportation practitioners at all levels with better tools to inform planning, design, and operations decisions to improve pedestrian and bicycle safety in the future. The lack of explicit consideration of pedestrian and bicycle safety in the HSM has primarily been due to insufficient data sources available to develop reliable pedestrian and bicycle SPFs. Various data sources are required to evaluate the safety of pedestrian and bicycle modes, including observed crash frequency data, exposure data, and infrastructure data. While crash, volume, and roadway inventory data are regularly tracked and documented for motor vehicles, several issues and barriers prevent analogous data for pedestrian and bicycle modes to be as well-documented. The two most comprehensive national crash frequency databases—the Fatality Analysis Reporting System and the National Automotive Sampling System General Estimates System—have been assembled based on police-reported crashes. Similarly, individual states maintain their own police-reported crash databases. While such national and state databases provide a good source for police-reported crashes, they do not account for crashes and injuries that occur but are not reported. Pedestrian and bicycle crashes are often underreported, especially for minor injuries; for example, some sources estimate that up to 20 percent of pedestrian crashes and 10 percent of bicyclist crashes are underreported (Agran, Castillo, and Winn 1990). On the exposure side, transportation agencies generally do not have well-developed programs to collect pedestrian and bicycle volumes on their roadways. Instead, detailed exposure data on the number of pedestrians and bicyclists using a facility are often collected manually, if at all, on just a subset of facilities. Common barriers to collecting pedestrian and bicycle count data include lack of staff time or volunteer interest and funding limitations or cutbacks, as manual data collection can be very costly (Ryus et al. 2014a). Hence, with limited funds, pedestrian and bicycle count data are typi- cally only collected for short durations and are primarily used to conduct studies for the safety of school zone crossings or for developing traffic signal timings (Cottrell and Pal 2003). Short-term pedestrian and bicycle count data are not ideal for developing SPFs. Automated systems that utilize various technologies, such as video, piezoelectric sensors, ultrasonic sensors, microwave radar, and laser scanners, have been used to obtain continuous pedestrian and bicycle volumes. In some cases, these continuous counts have been used to develop adjustment factors for time of day, day of week, and month to scale short-term counts, making them more suitable to predict the safety performance of pedestrians and bicyclists (Ryus et al. 2014b; Hughes et al. 2000; Zhao and Thorpe 1999; Oren et al. 1997; Nanda and Davis 2002; Suard et al. 2006; Bu and Chan 2005). To better understand pedestrian and bicyclist exposure, census data and/or household travel surveys can be used to sample the population to obtain detailed information on the usage of all modes, along with demographic information. Household travel surveys are done both at the national level, such as the National Household Travel Survey (NHTS), and at the local level through different metropolitan transportation agencies. While the NHTS covers a larger area, metropolitan travel surveys can provide more specific information about a given region. These types of surveys have their shortcomings. Typically, they only include work trips, and multi- modal trips are often omitted, leaving pedestrian and bicycle trips misrepresented. Most transportation agencies have electronic roadway inventory databases that include road- way characteristics such as the number of through lanes, lane widths, and shoulder widths. Fewer transportation agencies have intersection inventory databases that include features such as type of traffic control, number of approaches, and presence of turn lanes; even fewer agencies collect

6 Pedestrian and Bicycle Safety Performance Functions data on pedestrian and bicycle facilities (e.g., presence of bike lanes, buffered bike lanes, shoul- ders, sidewalks, marked crosswalks, raised medians, transit stops, etc.). The lack of data and poor quality of pedestrian and bicycle crashes, exposure, and inventory data make modeling pedestrian and bicycle crashes difficult. The need for comprehensive crash prediction models in the HSM to estimate the expected frequencies of pedestrian and bicycle crashes has been identified as a critical gap in the cur- rent state of practice since the HSM was published in 2010, and even before. Since 2004, the Federal Highway Administration (FHWA) Office of Safety has been working to aggressively reduce pedestrian deaths by focusing extra resources on the cities and states with the highest pedestrian fatalities and/or fatality rates. More and more agencies have been collecting data to improve pedestrian and bicycle safety in recent years through national programs such as FHWA’s “Pedestrian and Bicyclist Focused Approach to Safety” (states and cities); the U.S. Department of Transportation’s (USDOT) “Safer People, Safer Streets” initiative; FHWA’s approach to include information on nonmotorized traffic counting in the Traffic Monitoring Guide (TMG) (FHWA 2016); and initiatives by many local and city agencies and others. This final report presents research that utilized traditional and nontraditional data sources to develop pedestrian and bicycle SPFs. These SPFs will allow pedestrian and bicycle safety to be more explicitly incorporated into the HSM crash prediction methodology. Such models are critical for the HSM to remain a key safety prediction tool for application by highway agencies in the future. 1.2 Research Objective and Scope The objective of this research was to develop pedestrian and bicycle SPFs for transporta- tion practitioners at all levels to better inform planning, design, and operations decisions. This included the development of pedestrian and bicycle SPFs for a wide range of site types, including roadway segments and intersections in both urban/suburban and rural areas. This research addressed a broad range of issues related to evaluating pedestrian and bicycle safety, such as, but not limited to, the following: • Analyzing barriers to collecting pedestrian and bicycle safety performance data and developing performance-based decisions in the United States. • Documenting and evaluating domestic and international best practices that overcome barriers to collecting pedestrian and bicycle safety data, including traditional, nontraditional, and sur- rogate data sources at systemwide and local levels. • Documenting processes used to access and link pedestrian and bicycle data sources. • Testing and evaluating the application of identified best practices and linkage processes in a pilot study within a U.S. community. • Identifying data collection and analytical methods for use in the development of pedestrian and bicycle SPFs. • Developing and validating pedestrian and bicycle SPFs. • Developing a suite of data-driven tools (e.g., spreadsheets, software, and checklists) based on the research results to incorporate into the HSM. The results of the research are recommended for incorporation into the second edition of the HSM and associated tools. The first edition of the HSM uses the terms “vehicle-pedestrian crashes” and “vehicle-bicycle crashes” to identify crashes involving collisions between pedestrians and motor vehicles and between bicycles and motor vehicles, respectively. The first edition of the HSM also used the term

Introduction 7   “vehicle” as equivalent to “motor vehicle.” In fact, most state traffic codes designate a bicycle as a vehicle (specifically, a nonmotorized vehicle). To avoid the incorrect and unintended implica- tion that a bicycle is not a vehicle, throughout this report, the term “pedestrian crashes” refers to collisions involving pedestrians and motor vehicles, and the term “bicycle crashes” refers to collisions involving bicycles and motor vehicles. 1.3 General Research Approach The first step toward accomplishing the research objective was to summarize the state of prac- tice and gather information related to estimating pedestrian and bicycle safety performance. To do so, the research team reviewed and summarized information on barriers to collecting pedestrian and bicycle safety performance data and developing performance-based decisions; best practices for overcoming barriers to collecting pedestrian and bicycle safety data; processes used to access and link pedestrian and bicycle data sources; methods for estimating pedestrian and bicycle exposure; and methods for estimating pedestrian and bicycle safety performance. The research team also conducted a survey of state and local transportation agencies, practitio- ners, and researchers to learn about past experiences, challenges, and best practices regarding the collection of pedestrian and bicycle safety performance data; prior experience with the HSM; priorities for developing pedestrian and bicycle SPFs; and ongoing data collection efforts, data availability, and willingness of an agency to contribute to this research. In addition, the research team identified potential data sources for developing pedestrian and bicycle SPFs. Based on the literature review, a survey of practice, and the search of potential data sources, the research team developed a work plan to achieve the research objective. The work plan consisted of executing three separate approaches to collecting data and devel- oping pedestrian and bicycle SPFs for roadway segments and intersections, as follows. • Develop Pedestrian and Bicycle SPFs Incorporating Available Exposure Data for Pedes- trians and Bicyclists As part of this work plan, the research team developed pedestrian and bicycle SPFs using traditional crash-based modeling techniques. The focus was on developing pedestrian and bicycle SPFs for urban roadway segments and intersections for which pedestrian and bicycle exposure data were available or could be estimated. This work plan did not address SPFs for rural areas, as limited exposure data for pedestrians and bicyclists are available in rural areas. The results of this work plan could be considered for potential use in the HSM Part C predic- tive methods chapter for urban and suburban arterials (i.e., HSM Chapter 12) or for potential use in the Part B network screening chapter. • Develop an Approach to Pedestrian and Bicycle Crash Prediction for the HSM based on Procedures Implemented in the U.S. Road Assessment Program (usRAP) The U.S. Road Assessment Program (usRAP) is a safety management tool used to rate the safety of a roadway based on an assessment of the presence and condition of roadway, roadside, and intersection design elements and to identify cost-effective countermeasures to reduce fatal and serious injury crashes (usRAP, n.d.). usRAP was developed cooperatively with its international partner, the International Road Assessment Program (iRAP). The crash prediction methodology incorporated in usRAP was developed for worldwide application. As part of this work plan, the crash prediction methodology to estimate pedestrian and bicycle crashes incorporated in usRAP was adapted to better fit with highway safety practice in the U.S., and the terminology and format were modified for consistency with the HSM. Models were adapted for potential use in estimating pedestrian and bicycle crashes along roadways and at intersections in both urban and rural areas. The results of this work plan could be considered for potential use in the HSM Part C predictive methods chapters for rural two-lane roads (i.e., HSM Chapter 10), rural multilane highways (i.e., HSM Chapter 11), and

8 Pedestrian and Bicycle Safety Performance Functions urban and suburban arterials (i.e., HSM Chapter 12) and/or for potential use in the forthcoming chapter on pedestrians and bicyclists planned for HSM2. • Develop Models to Estimate Pedestrian and Bicycle Safety Performance Based on Crash Data in the Absence of Pedestrian and Bicycle Exposure Data As part of this work plan, the research team developed models to estimate the potential for pedestrian or bicycle crashes occurring along roadway segments and at intersections when pedestrian or bicycle exposure data are not available. Many agencies do not collect pedestrian or bicycle exposure data, so such models may be of particular interest to these agencies. Models were developed to estimate the potential for pedestrian or bicycle crashes along roadway seg- ments and at intersections in both urban and rural areas. The results of this work plan could be considered for potential use in the forthcoming new chapters on pedestrians and bicyclists and systemic safety management planned for HSM2. In addition, three spreadsheet tools were developed and/or updated to incorporate the pedes- trian and bicycle SPFs for use with HSM procedures. The spreadsheets—model analysis for rural multilane highways, rural two-lane roads, and urban and suburban arterials—are available on the National Academies Press website (nap.nationalacademies.org) by searching for NCHRP Research Report 1064. 1.4 Outline of Report This final report presents an overview of the work conducted to develop pedestrian and bicycle SPFs for the HSM. The remainder of this report is organized as follows: • Section 2: Literature Review and Survey of Practice • Section 3: Development of Pedestrian and Bicycle Models Incorporating Available Pedestrian and Bicyclist Exposure Data • Section  4: Development of Pedestrian and Bicycle Models Based on Road Assessment Program Methodology • Section 5: Development of Pedestrian and Bicycle Models in the Absence of Pedestrian and Bicyclist Exposure Data • Section 6: Conclusions, Recommendations, and Future Research • References • Abbreviations and Acronyms

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Each year, national crash studies have estimated that while overall traffic fatalities are decreasing, the percentages of those fatalities among pedestrians and cyclists are increasing.

NCHRP Research Report 1064: Pedestrian and Bicycle Safety Performance Functions, from TRB's National Cooperative Highway Research Program, presents state departments of transportation and other transportation professionals with an update of pedestrian and bicycle safety performance functions (SPFs).

Supplemental to the report are three spreadsheet tools that address SPFs on rural multilane roads, rural two-lane roads, and urban/suburban arterials.

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