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From page 77... ... 77 This chapter introduces the general methodology for quantifying safety performance at the corridor level. The methodology provides a structured approach to incorporate accessmanagement-related variables in estimating the crash frequency, by crash type and severity, for urban and suburban corridors. Read the entire page →
From page 78... ... 78 Application of Crash Modification Factors for Access Management detailed procedure for aggregating individual segment- and intersection-level crash predictions into a corridor-level prediction. If one or more of the three conditions previously mentioned are not met, then it is more appropriate to estimate the safety performance of the corridor using corridor-level prediction methods. Read the entire page →
From page 79... ... Predictive Method for Corridor-Level Analysis 79 Appendix D) Read the entire page →
From page 80... ... 80 Application of Crash Modification Factors for Access Management of different alternatives or if the crash history is unavailable or not applicable, then Analysis Level 1 (relative comparison of safety performance) is appropriate. Read the entire page →
From page 81... ... Predictive Method for Corridor-Level Analysis 81 The results are presented as the expected crash frequency per year for each alternative. The results from this analysis may be used to compare the expected number of crashes by type among various scenarios and can be used in an economic evaluation (e.g., benefit-cost analysis) Read the entire page →
From page 82... ... -- Not applicable. Crash Type Variables Available for Specified Land Use Applicable Model (Table No.) Read the entire page →
From page 83... ... Predictive Method for Corridor-Level Analysis 83 Variables for the equations shown in Figures 85 and 86 are defined as follows: • intercept = coefficient estimated for the model to account for unobserved variables. • Region = coefficient estimated for the model when the applicable region is North Carolina or Minnesota; a value of 0 is used if the applicable region is Northern California or Southern California. Read the entire page →
From page 84... ... 84 Application of Crash Modification Factors for Access Management – In some cases, explanatory variables are included for a specific crash type but not for the land use of interest. Further consideration of these variables in this section follows. Read the entire page →
From page 85... ... Predictive Method for Corridor-Level Analysis 85 corridor length or AADT changes in Alternative B, these changes are considered in isolation. The appropriate model for considering corridor length or AADT changes is identified in the "Applicable Base Model for Extrapolation and EB Method" column of Tables 69 through 71. Read the entire page →
From page 86... ... 86 Application of Crash Modification Factors for Access Management Step 4.1.4: Estimated Safety Impacts The results of Steps 4.1.2 and 4.1.3 can be used to compare the predicted crashes per year for Alternative A and Alternative B The results may be presented as the difference or the percent change in predicted crashes per year. Read the entire page →
From page 87... ... Predictive Method for Corridor-Level Analysis 87 Step 4.2.2d: Estimated EB Correction Factor. The EB correction factor is calculated as the expected crashes for existing conditions (Step 4.2.2c) Read the entire page →
From page 88... ... 88 Application of Crash Modification Factors for Access Management from models related to a different land use) Read the entire page →
From page 89... ... Predictive Method for Corridor-Level Analysis 89 Step 4: Select Applicable Model(s) and Perform Analysis Table 69 presents the applicable models for mixed land use. Read the entire page →
From page 90... ... 90 Application of Crash Modification Factors for Access Management in Chapter 4. Recall from Chapter 4, using Predictive Method Option 1 (i.e., combine segment- and intersection-level results) Read the entire page →
From page 91... ... Predictive Method for Corridor-Level Analysis 91 Step 2: Select Crash Types and Variables of Interest As noted in the problem definition, right-angle crashes are of interest. In this case, the variables of interest are proportion of full development (PROPFULLDEV) Read the entire page →
From page 92... ... 92 Application of Crash Modification Factors for Access Management Step 4.1.3: Calculations for Extrapolated Variables. There are no extrapolated variables, so this step is not applicable. Read the entire page →
From page 93... ... Predictive Method for Corridor-Level Analysis 93 Step 3: Select Analysis Level of Interest It is desired to estimate the relative safety of two alternatives, one of which is the do-nothing alternative (i.e., existing conditions) Read the entire page →
From page 94... ... 94 Application of Crash Modification Factors for Access Management The following are the data for the proposed condition (Alternative B) : • Corridor length = 4 miles (unchanged) Read the entire page →
From page 95... ... Predictive Method for Corridor-Level Analysis 95 change in ACCDENS is 0.26 crashes/year (28.35 crashes/year – 28.09 crashes/year) , and the change in total predicted crashes related to the change in PROPNODEV is 4.91 crashes/year (79.52 crashes/year – 74.61 crashes/year) Read the entire page →
From page 96... ... 96 Application of Crash Modification Factors for Access Management Step 4: Select Applicable Model(s) and Perform Analysis Table 69 presents the applicable models for various crash types in mixed land use. Read the entire page →
From page 97... ... Predictive Method for Corridor-Level Analysis 97 the calculations of predicted right-angle crashes per year for existing and proposed conditions, respectively, based on the coefficients in Table E-11. Right-Angle Crashes: Predicted Right-Angle Crashes/Year (Existing) Read the entire page →
From page 98... ... 98 Application of Crash Modification Factors for Access Management Sample Problem 8 Compare the expected crashes for two alternatives to select the most appropriate alternative. Problem Definition For a mixed-use corridor, a proposal has been made to increase the number of driveways by five and the number of unsignalized intersections by one. Read the entire page →
From page 99... ... Predictive Method for Corridor-Level Analysis 99 the difference in expected crashes is to be compared with the difference in costs of the two alternatives. In this case, Analysis Level 2 is applicable because the objective is to estimate the expected crashes for the given alternatives. Read the entire page →
From page 100... ... 100 Application of Crash Modification Factors for Access Management Step 4.2.2b: Estimated EB Weight. Figure 110 shows the calculation of w. Read the entire page →
From page 101... ... Predictive Method for Corridor-Level Analysis 101 Step 4.1.3 is Calculations for Extrapolated Variables. There are no extrapolated variables, so this step is not applicable. Read the entire page →
From page 102... ... 102 Application of Crash Modification Factors for Access Management Step 4.2.4: Estimated Safety Impacts. The results are provided as the expected crash frequencies per year for the crash types selected under both alternatives. Read the entire page →
From page 103... ... Predictive Method for Corridor-Level Analysis 103 Step 1: Select Land Use and Region This is a commercial corridor. After reviewing the summary statistics for commercial use in each of the four regions from which the models were developed and comparing them to the local data, it is determined that the corridor is most comparable to the data from Minnesota. Read the entire page →
From page 104... ... 104 Application of Crash Modification Factors for Access Management • 10 unsignalized intersections and 25 driveways: ACCDENS = 14.0 access points/mile (unchanged) Read the entire page →
From page 105... ... Predictive Method for Corridor-Level Analysis 105 Step 4.1.3d: Baseline Predicted Right-Angle Crashes/Year for Proposed Conditions. The baseline predicted crashes for the proposed conditions are estimated using the base model (Table E-24) Read the entire page →
From page 106... ... 106 Application of Crash Modification Factors for Access Management To facilitate such an assessment, Appendix F provides coefficients from the correlation matrix between the variables of interest that do not appear in any models and the various crash types by land use. Correlation coefficients range between –1.0 and 1.0. Read the entire page →
From page 107... ... Predictive Method for Corridor-Level Analysis 107 Example of Inconsistent and Illogical Effects Several of the variables in Appendix F are related to the presence of left-turn lanes, such as the number of signalized intersections with a left-turn lane on the mainline (NOLTLSIG) Read the entire page →

From page 77...

... 77 This chapter introduces the general methodology for quantifying safety performance at the corridor level. The methodology provides a structured approach to incorporate accessmanagement-related variables in estimating the crash frequency, by crash type and severity, for urban and suburban corridors.