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Pedestrian and Bicycle Safety Performance Functions (2023)

Chapter: Section 6 - Conclusions, Recommendations, and Future Research

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Page 287
Suggested Citation:"Section 6 - Conclusions, Recommendations, and Future Research." 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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Page 287
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Suggested Citation:"Section 6 - Conclusions, Recommendations, and Future Research." 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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Page 288
Page 289
Suggested Citation:"Section 6 - Conclusions, Recommendations, and Future Research." 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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Page 289

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287   6.1 Conclusions and Recommendations The following conclusions and recommendations have been developed in this research: 1. Pedestrian and bicycle SPFs presented in this report have been developed for use in the HSM to help inform planning, design, and operation decisions by transportation practitioners at all levels. The SPFs in Section 3 of this report have been developed in a consistent manner (i.e., using negative binomial regression analysis) with existing SPFs in HSM Part C, while the SPFs in Section 4 have been developed in a nontraditional approach for use in HSM Part C. Together, these SPFs are comprehensive in their ability to address a wide range of road types and intersection configurations and traffic control types in rural and urban and suburban areas, and the new SPFs are more sensitive to site-specific conditions that influence pedestrian and bicycle crashes than existing HSM models and provide additional assistance for evaluating site-specific effects of proposed projects intended to improve pedestrian and bicycle safety. 2. Most of the SPFs developed for potential use in HSM Part C appear compatible with existing models in HSM Part C. At certain levels of exposure for either motorized or nonmotorized traffic volumes, one or two of the SPFs predicted higher crash frequencies for pedestrians than for multiple- and single-vehicle crashes combined, which is not a logical result. For the majority of the SPFs, given reasonable exposure levels for both motorized and nonmotorized traffic volumes, the pedestrian and bicycle SPFs developed in this research provide pre- dicted values for pedestrian and bicycle crashes of the order of magnitude of what would be expected relative to total crashes (i.e., multiple- and single-vehicle crashes). However, even with introduction of the facility-type factor for use with the modified RAP models, both types of SPFs developed for potential use in HSM Part C will likely need some level of additional calibration to be compatible with the existing HSM models for multiple- and single-vehicle crashes. This will be necessary so that the predicted values for pedestrian and bicycle crashes will be of the order of magnitude of what would be expected relative to total crashes for a given site type. 3. The binary logistic regression models presented in Section 5 that estimate the probability of pedestrian and bicycle crashes, without the use of direct estimates of pedestrian and bicycle volumes (e.g., AADP, AADB, peak-hour pedestrian or bicycle volumes), provide trans- portation practitioners with a list of factors that either increase or decrease the potential for pedestrian and bicycle crashes. Transportation practitioners can use these factors for network screening purposes and to help inform design decision. 4. During the initial phase of the research, consideration was given to barriers to collecting pedestrian and bicycle safety performance data; of particular interest was the concern of underreporting of pedestrian and bicycle crashes. In fact, underreporting of crashes for motorized and nonmotorized modes is an issue that all transportation agencies face. During S E C T I O N 6 Conclusions, Recommendations, and Future Research

288 Pedestrian and Bicycle Safety Performance Functions work plan development and development of the modeling approaches, consideration was given to how underreporting of pedestrian and bicycle crashes could be incorporated into the pedestrian and bicycle crash prediction models that would be developed as part of this research, but given the current state of knowledge and practice, no logical and defensible approach was identified that would provide reliable results. Thus, as with all existing HSM models, the pedestrian and bicycle SPFs developed as part of this research do not account for underreporting of pedestrian and bicycle crashes. 6.2 Future Research The following future research needs have been identified throughout this research: 1. Future research is necessary to further evaluate approaches to defining boundaries of an intersection for purposes of assigning pedestrian and bicycle crashes to the intersection for model development. In this research pedestrian and bicycle crashes were assigned to inter- sections if the crash was located within 75 ft of the center of the intersection, and the crash was designated as intersection or intersection-related. Especially for intersection configura- tions that have a large footprint, a consistent approach for assigning pedestrian and bicycle crashes to intersections for crash prediction and comparison of alternative intersection con- figurations is necessary. 2. This research primarily focused on developing pedestrian and bicycle SPFs for road types and intersection types/configurations addressed in the first edition of the HSM, Part C Chapter 10 (Rural Two-Lane, Two-Way Roads), Chapter 11 (Rural Multilane Highways), and Chapter 12 (Urban and Suburban Arterials). As additional site types are added to the HSM, research will be necessary to develop additional pedestrian and bicycle SPFs to address the new site types. One approach will be to make additional modifications to the RAP models to address the new site types, but development of pedestrian and bicycle SPFs using tradi- tional approaches (i.e., negative binomial regression analysis) should also be considered. 3. Research is needed to address the underreporting of crashes in the HSM predictive method and models. This issue goes beyond simply addressing underreporting of pedestrian and bicycle crashes and should address both motorized and nonmotorized modes. 4. In this research, consideration was given to modeling pedestrian and bicycle crashes by crash types. In particular for roadway segments, consideration was given to modeling pedestrian crashes that occurred while pedestrians were walking along the roadway separately from crashes involving pedestrians crossing the road; consideration was also given to modeling driveway-related bicycle crashes separately from bicycle crashes that occurred riding along the road. For intersections, consideration was given to modeling crashes involving through movements by motor vehicles separately from crashes involving left-turning movements by motor vehicles. However, limitations in the crash data prohibited such analyses. Future research could be conducted to develop pedestrian and bicycle SPFs by crash types for poten- tial consideration in the HSM. 5. Engineering judgment leads to the belief that installation of sidewalks along a road should reduce pedestrian crashes, and, within the modified RAP methodology presented in this report, provision of sidewalks is one of the treatments that provides the greatest benefit to pedestrians [and is supported through research iRAP Road Attribute Risk Factors: Sidewalk Provision (iRAP 2013q)]. However, in development of the pedestrian SPFs using negative binomial regression analysis, one of the preliminary models for urban two-lane roads sug- gested that provision of sidewalks on both sides of the road may increase pedestrian crashes. This was a counterintuitive finding but could be explained by the fact that the provision of sidewalks on both sides of the street may increase the number of pedestrian crossings at midblock locations, increasing pedestrian exposure and pedestrian crash frequency. Additional investigation into this counterintuitive finding is recommended.

Conclusions, Recommendations, and Future Research 289   6. Engineering judgment also leads to the perception that an increase in speed of motor vehicle traffic should likely increase the frequency of pedestrian and bicycle crashes, and, within the modified RAP methodology presented in this report, the models predict an increase in pedestrian and bicycle crashes with an increase in motor vehicle speeds through use of the motor vehicle traffic speed factors. However, in development of the pedestrian and bicycle SPFs using negative binomial regression analysis, preliminary models for pedestrian crashes for four-lane undivided and divided roads, pedestrian crashes for one-way roads, and bicycle crashes for one-way roads suggested that pedestrian and bicycle crashes decrease with an increase in motor vehicle speeds. This was a counterintuitive finding that could not be explained. Additional investigation into this counterintuitive finding is recommended. 7. Roundabouts are a proven safety countermeasure that reduces speeds and conflicts, resulting in a substantial reduction of fatal-and-injury crashes (FHWA 2021). However, limited infor- mation on the safety performance of pedestrians and bicyclists is available. Therefore, future research is recommended on pedestrian and bicycle safety performance at roundabouts.

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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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