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From page 156...
... 156 Chapter 7. Development of Models for Use in HSM Crash Prediction Methods: Three-Leg Intersections Where the Through Movements Make Turning Maneuvers at the Intersections This section describes the development of crash prediction models for three-leg intersections, where the through movement makes a turning maneuver at the intersection, and presents the final models recommended for incorporation in the second edition of the HSM.
From page 157...
... 157 • The traffic control at the intersection was something other than stop control or stop except right turn • The number of intersection legs was not three • A private driveway was located at the intersection • One or more of the approaches to the intersection was a private/commercial access • One or more of the intersection legs was a one-way street Each intersection that was initially deemed appropriate for inclusion in model development was given a unique identification code and included in a refined database for detailed data collection. Three types of data were collected for each intersection during detailed data collection: site characteristic, crash, and traffic volume data.
From page 158...
... 158 Table 71. Site characteristic variables collected for three-leg intersections where the through movements make turning maneuvers at the intersections (Continued)
From page 159...
... 159 Curve length and radius were also of potential interest for model development. The use of some of these site characteristics is discussed later in the SPF model development section (Section 7.3)
From page 160...
... 160 Table 72. Major- and minor road AADT and total entering volume statistics for three-leg intersections where the through movements make turning maneuvers at the intersections Major Road AADT (veh/day)
From page 161...
... 161 Crash Counts Intersection crashes were defined as those crashes that occurred within 250 ft of the intersection and were classified as "at intersection" or intersection-related, consistent with recommended practice in the HSM for assigning crashes to an intersection. Of the 211 intersections used in model development, 87 intersections (41.2%)
From page 162...
... 162 Table 74. Crash counts by crash severity for urban three-leg intersections where the through movements make turning maneuvers at the intersections State Date Range Number of Sites Number of Site Years Time of Day All Crashes Combined SV Crashes Multiple-Vehicle Crashes Pedestrian Crashes Bicycle Crashes Total FI PDO Total FI PDO Total FI PDO FI FI KY 2014-2018 19 95 All 49 5 44 15 4 11 34 1 33 0 0 Night 11 3 8 7 3 4 4 0 4 0 0 OH 2008-2017 7 70 All 67 21 46 34 11 23 33 10 23 0 0 Night 17 4 13 15 4 11 2 0 2 0 0 PA 2013-2017 21 105 All 61 26 35 29 11 18 32 15 17 2 0 Night 32 13 19 19 8 11 13 5 8 2 0 All States 2008-2018 47 270 All 177 52 125 78 26 52 99 26 73 2 0 Night 60 20 40 41 15 26 19 5 14 2 0
From page 163...
... 163 Crash counts are tallied by collision type and manner of collision across all states in Table 75 for rural three-leg turning intersections and in Table 76 for urban three-leg turning intersections. Table 75.
From page 164...
... 164 Where: Nspf int = predicted average crash frequency for an intersection with base conditions (crashes/year) AADTmaj = AADT on the major road (veh/day)
From page 165...
... 165 The SPF portion of Nbi, Nspf int, is the sum of two more disaggregate predictions by collision type, as shown in Equation 6.
From page 166...
... 166 For the rural three-leg turning intersection model, presence of intersection lighting was found to be the only intersection characteristic that was statistically significant. Since there was an abundance of site-years, it was decided to exclude all intersections with lighting and derive a model based only on unlighted intersections.
From page 167...
... 167 Figure 57. Graphical representation of the SPF for total crashes at three-leg turning intersections on rural two-lane roadways (based on model for total crashes in Equation 53)
From page 168...
... 168 Table 79. Distributions for collision type and manner of collision and crash severity at three-leg turning intersections on rural two-lane roadways Collision Type Percentage of Total Crashes by Collision Type Total FI PDO Single-Vehicle Crashes Collision with animal 7.1 0.0 11.2 Collision with bicycle 0.0 0.0 0.0 Collision with pedestrian 0.0 0.0 0.0 Overturned 3.8 6.9 2.1 Ran off road 57.1 61.1 54.9 Other SV crash 3.9 3.8 3.9 Total SV crashes 71.9 71.8 72.1 Multiple-Vehicle Crashes Angle collision 18.1 19.8 17.2 Head-on collision 2.8 3.8 2.1 Rear-end collision 2.2 1.5 2.6 Sideswipe collision 3.9 2.3 4.7 Other MV collision 1.1 0.8 1.3 Total MV crashes 28.1 28.2 27.9 Total crashes 100.0 100.0 100.0 Table 80 shows the coefficients and associated statistics of the final SPFs for urban three-leg turning intersections.
From page 169...
... 169 Figure 58. Graphical representation of the SPF for total MV crashes at three-leg turning intersections on urban and suburban arterials (based on model for total crashes in Equation 53)
From page 170...
... 170 Figure 60. Graphical representation of the SPF for PDO multiple-vehicle crashes at three-leg turning intersections on urban and suburban arterials (based on model for total crashes in Equation 53)
From page 171...
... 171 Figure 62. Graphical representation of the SPF for FI SV crashes at three-leg turning intersections on urban and suburban arterials (based on model for total crashes in Equation 53)
From page 172...
... 172 Table 81 (similar to Table 79 for rural intersections) provides percentages of total crashes by collision type and severity level for urban three-leg turning intersections.
From page 173...
... 173 Where: fpedi = pedestrian crash adjustment factor for intersection type i Table 82. Pedestrian crash adjustment factor for three-leg turning intersections on urban and suburban arterials Intersection Type Pedestrian Crash Adjustment Factor (fpedi)
From page 174...
... 174 potentially more time to assess gaps once vehicles on the uncontrolled approach(es) are seen.
From page 175...
... 175 Figure 65. Comparison of new crash prediction model to existing model in HSM: 3STT vs 3ST on urban and suburban arterials (MV-total crashes)
From page 176...
... 176 Figure 66. Comparison of new crash prediction model to existing model in HSM: 3STT vs 3ST on urban and suburban arterials (MV FI crashes)
From page 177...
... 177 Figure 67. Comparison of new crash prediction model to existing model in HSM: 3STT vs 3ST on urban and suburban arterials (SV-total crashes)
From page 178...
... 178 Figure 68. Comparison of new crash prediction model to existing model in HSM: 3STT vs 3ST on urban and suburban arterials (SV FI crashes)
From page 179...
... 179 identified for potential use with the crash prediction models for rural three-leg turning intersections was the CMF for intersection lighting based on the work by Elvik and Vaa (2004) , which is identified for use with the intersection crash prediction models in Chapters 10, 11, and 12 of the first edition of the HSM.
From page 180...
... 180 Table 84. CMF coefficients for curve CMF at three-leg turning intersections on urban and suburban arterials SPF to which the CMF applies Coefficients used in Equation 55 A b MV-Total -0.014 0.017 MV FI -0.014 0.019 MV PDO -0.017 0.020 SV-Total 0a 0.009 SV FI 0a 0.013 SV PDO 0a 0.008 a Curve radius was not found to be statistically significant in predicting SV crashes Tables 85-90 show computed curve CMF values for various crash types and severities by various levels of curve length and radius.
From page 181...
... 181 Table 88. Curve CMF values for SV total crashes Curve Radius (ft)
From page 182...
... 182 7.6 Summary of Recommended Models for Incorporation in the HSM In summary, several crash prediction models were developed for three-leg intersections where the through movements make turning maneuvers at the intersections for consideration in the second edition of the HSM, including models for: • Three-leg turning intersections on rural two-lane roadways • Three-leg turning intersections on urban and suburban arterials The final models recommended for inclusion in the second edition of the HSM are for total crashes on three-leg turning intersections on rural two-lane roadways (as shown in Table 77) and MV total, MV FI, MV PDO, SV total, and SV PDO crashes at three-leg turning intersections on urban and suburban arterials (as shown in Table 80)

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