Developing a Guide for Quantitative Approaches to Systemic Safety Analysis (2020) / Chapter Skim
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1 Introduction 1.1 Background Highway agencies have traditionally managed the safety improvement process by identifying and correcting high-crash locations ("hot-spots") , where concentrations of crashes and, often, patterns of crashes of similar types, were found.
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2 As part of this research, the research team developed a comprehensive guidance document that defines quantitative approaches to systemic safety analysis; contrasts systemic safety management approaches to traditional crash-history-based and policy-based safety management approaches; describe the tools available to highway agencies to implement systemic safety analysis; and defines the capabilities, advantages, disadvantages, and data requirements for each tool. The first edition on the American Association of State Highway and Transportation Officials (AASHTO)
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3 1.2 Summary of Primary Safety Management Approaches The three primary approaches to highway safety management include crash-history-based, systemic, and policy-based safety management approaches. These approaches vary in terms of the types, quantity, and quality of data required to carry them out; the types of treatments considered for application; and the types of crashes or safety concerns the transportation agency may address.
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4 other sites on the prioritized list. Sites that rise to the top of the priority list for potential safety improvement tend to be located on urban corridors and at urban intersections where traffic volumes are highest.
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5 Safety improvements may be made at sites to remedy specific crash types that may not occur again, even if no improvements are made. Implementation of higher-cost safety improvements at a limited number of sites may not effectively reduce crash frequency across the network (Gross et al., 2016)
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6 performance functions (SPFs) are used to calculate predicted and/or expected crash frequencies of target crash types at specific sites.
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7 Lighting Countermeasures are chosen to remedy target crash types and in conjunction address the crash contributing factors identified for the specific crash types of interest, and are then implemented at many sites where those crash contributing factors are present, regardless of previous crash history. Typically, one, two, or three proven, low-cost countermeasures are initially identified for consideration to address a particular target crash type.
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8 With this approach, it may be easier to more equally distribute safety funds regionally or across jurisdictions compared to programming safety improvements based solely on a crash-history-based safety management approach. This approach is adaptable based on available data.
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9 costs. Expected benefits may be estimated using a reliable crash modification factor (CMF)
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10 This final report, which documents the research process and findings. A comprehensive guidance document on the implementation of quantitative approaches to systemic safety analysis (intended as a companion document to this final report)
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11 1.4 Overview of Research Methodology The research in Project 17-77 was conducted in seven tasks as follows: Phase I Task 1: Review Literature Task 2: Review Current Practice Task 3: Develop Outline and Write Portions of Draft Guidance Document Task 4: Develop Work Plan Task 5: Prepare Interim Report Phase II Task 6: Execute Approved Work Plan Task 7: Prepare Final Deliverables In Task 1 the research team reviewed and summarized literature relevant to the objectives of this research. As part of this review, the research team (1)
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12 tasks. The interim report also included, as a standalone appendix, the draft guidance document as it stood at the completion of Task 3.
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