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From page 50... ... 50 Chapter 4 introduces the general methods for quantifying safety performance at the segment and intersection level. The segment- and intersection-level predictive method provides a structured approach to estimate crash frequency, by crash type and severity, for urban and suburban segments and intersections. Read the entire page →
From page 51... ... Predictive Method for Segment- and Intersection-Level Analysis 51 e Part C Predictive Method is an 18-step process, as dened in the Highway Safety Manual (1st Edition) and illustrated in Figure 16. Read the entire page →
From page 52... ... 52 Application of Crash Modification Factors for Access Management In general, the equation shown in Figure 17 represents the Part C Predictive Method for urban and suburban arterials. This equation includes five main components: (1) Read the entire page →
From page 53... ... Predictive Method for Segment- and Intersection-Level Analysis 53 The next section of this chapter focuses on Step 9 of the Part C Predictive Method, which involves selecting and applying an applicable SPF. Select and Apply an Applicable SPF Prior to selecting SPFs, it is important to understand the applicability of SPFs available in the Part C Predictive Method. Read the entire page →
From page 54... ... 54 Application of Crash Modification Factors for Access Management Figure 19. Predicted segment-related crash frequency for base conditions. Read the entire page →
From page 55... ... Predictive Method for Segment- and Intersection-Level Analysis 55 Figure 21 presents the SPF for single-vehicle segment crashes for base conditions from the Highway Safety Manual (1st Edition) Read the entire page →
From page 56... ... 56 Application of Crash Modification Factors for Access Management • nj = total number of driveways within the segment (both sides of road) of driveway type j. Read the entire page →
From page 57... ... Predictive Method for Segment- and Intersection-Level Analysis 57 Figure 24 presents the SPF for multivehicle intersection crashes for base conditions from the Highway Safety Manual (1st Edition) Read the entire page →
From page 58... ... 58 Application of Crash Modification Factors for Access Management The results from the equations in Figures 24 and 25 are combined to predict the average crash frequency of an individual intersection under base conditions (from the equation in Figure 23) Read the entire page →
From page 59... ... Predictive Method for Segment- and Intersection-Level Analysis 59 the Part C Predictive Method assumes each site is independent, which does not capture these potential interactions, and the segmentation process is not conducive to quantifying the safety impacts of interactions among sites. Interactions among access management features, particularly those related to access spacing and density, are more appropriately addressed through the corridor-level models in Chapter 5. Read the entire page →
From page 60... ... 60 Application of Crash Modification Factors for Access Management predictions for features on urban and suburban arterials related to access management. Refer to Chapter 3 of this guide for additional CMFs that could potentially be applied in the Part C Predictive Method. Read the entire page →
From page 61... ... Predictive Method for Segment- and Intersection-Level Analysis 61 CMFs for Right-Turn Lanes Table 59 presents the CMFs for right-turn lanes at urban and suburban arterial inter sections. The applicable CMF is applied to the total predicted crashes from the base SPF using the general equation from Figure 17, excluding vehicle-pedestrian and vehicle-bicycle crashes. Read the entire page →
From page 62... ... 62 Application of Crash Modification Factors for Access Management vehicle-bicycle crashes. The research indicates that predicted crashes increase at stop-controlled intersections where a ramp terminal is present within 1,500 feet; however, the results are not statistically significant, even at the 90-percent confidence level (i.e., CMF = 2.12 with standard error = 0.91) Read the entire page →
From page 63... ... Predictive Method for Segment- and Intersection-Level Analysis 63 Step 1: Predict Multivehicle Non-Driveway Collisions Figures 27 through 29 show the calculations to predict multivehicle non-driveway collisions for total, fatal and injury, and PDO crashes, respectively, based on the SPF from Figure 20 and coefficients from Table 50. Variable Existing Condition Proposed Condition Road type 3T 3T Length of segment 1.5 miles 1.5 miles AADT 11,000 vehicles/day 11,000 vehicles/day Type of on-street parking Parallel-commercial Parallel-commercial Median width Not present Not present Lighting Present Present Auto speed enforcement Not present Not present Major commercial driveways 0 10 Minor commercial driveways 10 0 Major industrial/institutional driveways 0 0 Minor industrial/institutional driveways 3 3 Major residential driveways 2 2 Minor residential driveways 15 15 Other driveways 0 0 Posted speed limit 35 mph 35 mph Roadside fixed object density 10 fixed objects/mile 10 fixed objects/mile Offset to roadside fixed objects 6 feet 6 feet Calibration factor 1 1 Source: AASHTO 2010. Read the entire page →
From page 64... ... 64 Application of Crash Modification Factors for Access Management Step 2: Predict Single-Vehicle Crashes Figures 32 through 34 show the calculations to predict single-vehicle collisions for total, fatal and injury, and PDO crashes, respectively, based on the SPF from Figure 21 and coefficients from Table 51. Figure 34. Read the entire page →
From page 65... ... Predictive Method for Segment- and Intersection-Level Analysis 65 Figures 38 and 39 show the calculations to separate the predicted total multivehicle drivewayrelated crashes by severity to obtain fatal and injury multivehicle driveway-related crashes (Nbrdwy(FI) Read the entire page →
From page 66... ... 66 Application of Crash Modification Factors for Access Management Lighting CMF Figure 43 shows the calculation of the CMF for lighting (CMF4r) Read the entire page →
From page 67... ... Predictive Method for Segment- and Intersection-Level Analysis 67 Step 7: Calculate Predicted Average Crash Frequency Figure 49 shows how to combine the previous calculations to estimate the predicted average crash frequency for existing conditions (Npredicted rs) Read the entire page →
From page 68... ... 68 Application of Crash Modification Factors for Access Management Figure 53 shows the calculation of the predicted total crash frequency for the proposed base conditions using the multivehicle driveway-related crashes from Figure 50 and the multivehicle non-driveway crashes and single-vehicle crashes from Figure 27 and Figure 32, respectively. Figure 51. Read the entire page →
From page 69... ... Predictive Method for Segment- and Intersection-Level Analysis 69 Sample Problem 2 Estimate the expected average crash frequency per year for a three-legged stop-controlled intersection located on an urban arterial, employing the EB method, and then estimate the change in expected average crash frequency per year for two proposed conditions: (1) a proposed right-turn lane on the major road and (2) Read the entire page →
From page 70... ... 70 Application of Crash Modification Factors for Access Management Figures 61 and 62 show the calculations to adjust the predicted fatal and injury multivehicle crashes and PDO multivehicle crashes to sum to the total multivehicle crashes. Variable Existing Condition Proposed Condition A (right-turn lane on major road) Read the entire page →
From page 71... ... Predictive Method for Segment- and Intersection-Level Analysis 71 There are no models for fatal and injury crashes at three-legged stop-controlled intersections. Figure 65 shows the calculation of fatal and injury crashes, which is based on the proportion of total crashes using a default proportion of fatal and injury crashes. Read the entire page →
From page 72... ... 72 Application of Crash Modification Factors for Access Management Combined CMF Figure 68 shows the calculation of the combined CMF value once all of the CMFs are calculated. Figure 68. Read the entire page →
From page 73... ... Predictive Method for Segment- and Intersection-Level Analysis 73 Manual (1st Edition) due to the difference in major road traffic volume. Read the entire page →
From page 74... ... 74 Application of Crash Modification Factors for Access Management Single-Vehicle Crashes Figure 76 shows the calculation of the weight factor for single-vehicle crashes (wsv) , which is used in the EB method. Read the entire page →
From page 75... ... Predictive Method for Segment- and Intersection-Level Analysis 75 Step 8: Estimate the Expected Average Crash Frequency for Proposed Condition A This step is related to Proposed Condition A (i.e., installation of a right-turn lane on a major road of a three-legged stop-controlled intersection) Read the entire page →
From page 76... ... 76 Application of Crash Modification Factors for Access Management Sample Problem 3 Estimate the predicted average crash frequency along a 1.5-mile urban two-lane arterial corridor with a TWLTL and 10 three-legged stop-controlled intersections. Problem Definition This scenario is based on the existing conditions in Sample Problem 1 and Sample Problem 2. Read the entire page →

From page 50...

... 50 Chapter 4 introduces the general methods for quantifying safety performance at the segment and intersection level. The segment- and intersection-level predictive method provides a structured approach to estimate crash frequency, by crash type and severity, for urban and suburban segments and intersections.