Crash Modification Factors in the Highway Safety Manual: A Review (2023)

Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

37   CMF Gap Analysis 10.1 Objective The objective was to conduct a CMF gap analysis that would identify CMF research needs to guide future CMF development efforts. To identify the gaps in CMF research, it was crucial to begin with a firm understanding of existing knowledge about CMFs and of what research was in progress to develop new CMFs. Additionally, it was important to understand the relative quality and applicability of existing and forthcoming CMFs. 10.2 Approach and Outcomes On the basis of a review of existing CMFs and CMFunctions from the CMF Clearinghouse, the project team developed the following list of 18 countermeasure categories: • Access management, • Advanced technology and intelligent transportation systems, • Alignments, • Bicyclists and pedestrians, • Delineation, • Highway lighting, • Interchanges, • Intersection geometry, • Intersection traffic control, • Pavement treatment and resurfacing, • Roadside, • Roadway, • Railroad crossing, • Shoulders, • Signs, • Bridges and structures, • Work zones, and • Other. Under each of these categories, the research team then identified similar countermeasures and organized them in countermeasure subcategories. For example, all CMFs related to changing the spacing or density of driveways along roadways were placed in the same group of counter­ measures, “Change Driveway Spacing/Density,” created under the category of access management. C H A P T E R 1 0

38 Crash Modification Factors in the Highway Safety Manual: A Review The team also identified the applicability of each CMF by some or all of the following elements (as applicable and available): • Area type: all, urban/suburban, and rural; • Intersection configuration: three­leg, four­leg, and more than four–leg; • Intersection traffic control: signal, stop, and roundabout; • Number of lanes: two lanes, four lanes, and other; and • Crash severity: On the basis of the KABCO scale, five levels of severity are possible: fatal (K), incapacitating injury (A), nonincapacitating injury (B), possible injury (C), and property damage only (PDO). CMFs were provided for the following categories of crash severity: KABCO, KABC, KAB, and PDO. For each subcategory of countermeasures, the average, maximum, and minimum CMF ratings were calculated. These rating values helped determine the overall quality of the CMFs under each subcategory. The team also counted the number of CMFs currently available for each subcategory separated by area type, intersection configuration, traffic control type, and number of lanes, where applicable, as well as crash severity. These CMF counts helped determine the gaps in terms of quantity (i.e., subcategories with no CMFs). Overall, the research team categorized and scored 7,407 CMFs from the CMF Clearinghouse that were reviewed and rated under this project. After summarizing all available CMFs and their quality (based on the mean and maximum and minimum CMF ratings) and quantity (number of CMFs by each subcategory), the project team conducted a search into ongoing research efforts, focusing primarily on NCHRP and FHWA, for potential CMFs that could be developed from these studies. The team identified a total of 29 active or upcoming NCHRP projects on the TRB website that appeared to be related to the 18 countermeasure categories and might produce more CMFs to fill some of the gaps. The team also searched the list of recent FHWA task orders and reached out to FHWA for additional information on recently completed and ongoing CMF development efforts. Overall, the team identified a total of 14 active or recently completed FHWA task orders that will likely produce more CMFs. It is important to note that a single project may cover more than one category. Appendix P has the detailed summary of the activities undertaken on this task. Inevitably, in this process, there are duplications due to semantic differences in identifying counter­ measures within and outside the clearinghouse. In Appendix P, footnotes are provided where such duplications were identified, but it is nevertheless still possible that an identified gap for a non­clearinghouse CMF may be filled by definitive information on CMFs that have a different name in the clearinghouse. Similarly, it is possible that an identified gap for a clearinghouse CMF may be filled by definitive information on CMFs that have a different name and fall under a different clearinghouse category. In short, the gaps identified in Appendix P will need confir­ mation as such before research to fill the gap is considered. Appendix P contains tables that provide summary information for each countermeasure to facilitate the identification of potential gaps. The summary information includes the number of CMFs in the clearinghouse, the range of ratings for these CMFs, and the number of CMFs applicable to each area type and crash severity level. Identified gaps are color­coded in the tables in Appendix P.