Crash Modification Factors in the Highway Safety Manual: A Review (2023) / Chapter Skim
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Pages 23-26
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From page 23... ...
23 Development of CMFunctions for Select Treatments 5.1 Background A key limitation of the HSM and the CMF Clearinghouse is the limited information regarding the variability in CMFs by application circumstances. It is difficult to think of any CMF of which it can categorically be said that the CMF would be constant from application to application.
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From page 24... ...
24 Crash Modification Factors in the Highway Safety Manual: A Review the CMFunctions. The original evaluation used an EB before–after method.
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Development of CMFunctions for Select Treatments 25 count is then used as the dependent variable, with the expected crashes as an offset in a count model that includes characteristics of application circumstances as independent variables. As in the case of metaregression, this approach can be used with individual sites, group of sites, or at the study level.
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From page 26... ...
26 Crash Modification Factors in the Highway Safety Manual: A Review • For multivehicle crashes on undivided roadways, the CMF for shoulder width was found to increase as AADT increased. • The CMFs estimated for shoulder width and median width imply the same change in crash frequencies for a unit change in the variable -- for example, that a change in median width from 2 ft to 8 ft has the same effect on crashes as a change from 8 ft to 14 ft.
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