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10 Determination of User Preferences and Practices In addition to a review of the existing methods in the HSM and CMF Clearinghouse, another key consideration is the preferences and practices of the CMF user community. CMF users include safety and design engineers, planners, researchers, academics, and other professionals at the national, state, and local levels. It is critical to consider how they currently use CMFs and how best to present CMF information in the HSM2. This task involved a questionnaire that was distributed electronically in 2015 and a focus group of experienced users that was conducted in February 2016. A summary on the findings is provided here. Further details are provided in Appendix B. 3.1 Selecting and Applying CMFs Focus group participants were asked how they selected CMFs when presented with multiple options. Many said that they prioritized CMFs that had high star ratings in the CMF Clearing house. They also said that they prioritized CMFs that were developed in the same geographic region or that closely matched the characteristics of the site of interest. There was also a concern expressed that some agencies (e.g., DOT districts) may often select a CMF that shows the greatest benefit, even if it does not match site conditions or is not highly rated. The results of the questionnaire showed that most respondents used both aggregate (total crash) and disaggregate (crash type and crash severity) CMFs, which they typically applied to modify historical crash values (the past 3â5 years of data) at the site of interest. This was true for all subgroups of positions represented among the respondents except researchers/teachers, who mostly applied CMFs to expected crashes produced from safety performance functions. When presented with quizÂtype scenarios, almost all questionnaire respondents selected the correct specific CMF to use in the given scenario. However, when presented with a scenario in which they had to apply a given CMF correctly to a given set of crash types, 81% applied it correctly. Most of the incorrect responses were due to the application of the specific crash type CMF to the total crashes at the site. Several focus group participants responded that CMF availability is a factor in project imple mentation, since they strive for a dataÂdriven approach, and that they desire to have a defensible backing for a decision to implement a safety treatment. If only a CMF with a low star rating is available for a given treatment in the CMF Clearinghouse, they might still use it but might not base highÂlevel projects on it. Most focus group participants indicated that they rarely or never used CMFunctions. They said this is because of the lack of CMFunctions that address the countermeasure of interest or match their site conditions. It is also because CMFs (point factors) are simpler, easier to communicate, and easier to use at a planning level. C H A P T E R 3
Determination of User Preferences and Practices 11 3.2 CMF Quality Questionnaire respondents indicated that they used information on CMF quality most of the time or always. Most of them indicated that they used this information to prioritize CMFs when selecting from multiple options. This agrees with the findings from the focus group, in which many participants mentioned the CMF star rating as one of their primary prioritization measures. Most focus group participants referred to CMF quality by star rating (from the CMF Clearinghouse) and said that they did not use the standard error value, though one person indi cated using standard errors to compute a range of potential CMF values. No one referred to using the HSM adjusted standard error as an indication of quality, and several even admitted that they really did not understand it. Focus group participants generally considered three stars to be a minimum acceptable level for selecting a CMF, but several said that they would use a CMF with a lower star rating if it was the only one available for the countermeasure of interest. They ideally preferred to see multiple highÂrated CMFs in agreement (close to the same value) before using a CMF estimate. Regarding the criteria used to rate the quality of a CMF, focus group participants said that a CMF should be given a lower rating if it does not have much accompanying detail (such as the type of crash to which it applies) or if it is a general CMF (for total crashes only). 3.3 Presentation of CMFs Most questionnaire respondents said that they would want to see all available CMFs pre sented for each specific condition (as opposed to only a single CMF). Written responses to the questionnaire generally indicated a preference for a curated directory of CMFs, in which there would be an indication of a recommended or practiceÂready CMF while all other avail able CMFs would still be listed. Focus group participants were generally in favor of presenting all CMFs available online, but a few indicated a desire for an HSMÂdesignated CMF for each countermeasure. They also mentioned showing the CMF as a range of values to indicate how reliable it was. Focus group participants said that it was very important to be able to understand the specific type of crash used in developing the CMF. Often the details or even the source document do not adequately explain how the researcher defined the crash type. Participants also said that it was important to have CMFs that addressed specific injury levels on the KABCO Injury Classification Scale [K = fatal (killed), A = incapacitating injury, B = nonincapacitating injury, C = possible injury, and O = property damage only]. 3.4 Future Content of the HSM Part D In response to a question about the future content of the HSM Part D, the highest percent age of questionnaire respondents (50%) preferred that the HSM not include CMFs in Part D but instead provide a stamp of approval to CMFs in the CMF Clearinghouse that meet the HSM reliability requirements. This was followed by 33% who preferred to see the HSM continue the existing format of Part D (i.e., inclusion of CMFs that meet the HSM reliability requirements). However, the answers by the respondentsâ position type were divided, with traffic safety engineers, traffic engineers, and researchers/teachers largely preferring that the HSM Part D not contain CMFs, and highway designers, transportation planners, and agency administrators preferring that the HSM continue to include CMFs in Part D. Focus group participants were generally in favor of presenting CMFs online in the CMF Clearinghouse. They reasoned that the website was more accessible to the CMF user community
12 Crash Modification Factors in the Highway Safety Manual: A Review and more up to date and that it provides the opportunity to dig deeper to see more details about any CMF. However, some also said there was value in having select CMFs appear in the published HSM, with reference to the CMF Clearinghouse for the list of all available CMFs. Regarding guidance in the HSM, questionnaire respondents almost unanimously indicated a desire for Part D to include guidance on how to apply CMFs in safety practice. About half of the respondents also wanted Part D to include guidance on how to develop CMFs in research studies. One focus group participant also mentioned a desire for guidance on selecting CMFs.
