Guidelines for the Development and Application of Crash Modification Factors (2022) / Chapter Skim
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D-1 Contents D-1 Introduction D-2 Software Requirements D-3 User Guide D-8 Example Application of CMF Regression Tool D-11 Example Application Continued Introduction The CMF Regression Software is a Microsoft Excel™ tool developed under NCHRP Project 17-63: Guidelines for the Development and Application of Crash Modification Factors that can be used to conduct a statistical evaluation of crash modification factors (CMFs) for a common treatment or change in site characteristic.
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D-2 Guidelines for the Development and Application of Crash Modification Factors crashes by severity type) so the conduct of Evaluation type 2 will require the analyst to obtain the desired information from one or more CMF research documents.
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User Guide for CMF Regression Software D-3 Model Description The model structure to be used is entered. Two choices are currently supported: "Model 1" and "User Defined." The structure of Model 1 is described in equation form in this section of the worksheet.
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D-4 Guidelines for the Development and Application of Crash Modification Factors Data Description The number of CMF observations is entered in the blue cell provided. The minimum number of observations must exceed by two the sum of the crash distribution and site characteristic variables.
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User Guide for CMF Regression Software D-5 Run Control Two gray buttons are provided to control the evaluation. These buttons are shown in Figure D3.
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D-6 Guidelines for the Development and Application of Crash Modification Factors (i.e., a small number of observed crashes)
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User Guide for CMF Regression Software D-7 desired level of confidence, it can be excluded from the regression model by entering "No" in the "Include" row of the Main worksheet. Average CMF After the "Analyze Data" button is clicked, the best-fit regression coefficients are used to compute the average CMF for each crash distribution category.
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D-8 Guidelines for the Development and Application of Crash Modification Factors If the analyst has chosen "User Defined" model in the Set Up worksheet, then the equation for the model is entered in each of the cells with a gray background. The desired equation must use Excel formula protocols.
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User Guide for CMF Regression Software D-9 The values obtained from the CMF Clearinghouse are listed in Table D2. There are eight CMFs (shown in Table D2)
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D-10 Guidelines for the Development and Application of Crash Modification Factors General Information Project description: Analyst: Date: Model Description Model 1 CMF = [p1 x CMF1 + p2 x CMF2 + ...
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User Guide for CMF Regression Software D-11 Step 3. Enter Values of the Site Characteristic Variables No site characteristic variables need to be examined to answer the question of interest, so this step is skipped.
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D-12 Guidelines for the Development and Application of Crash Modification Factors Step 1. Describe the Model and Database in the Set Up Worksheet The Set Up worksheet is used for this step.
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User Guide for CMF Regression Software D-13 Step 3. Enter Values of the Site Characteristic Variables The area type variable is categorical, so it is converted to an indicator variable (i.e., numeric binary format)
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D-14 Guidelines for the Development and Application of Crash Modification Factors The CMF for urban conditions is computed by entering a "1" in cell N11. The value "1" is used because this value was defined as representing urban conditions using the indicator variable described in Step 3.
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