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From page 57... ... 57 Chapter 3. Development of Models for Use in HSM Crash Prediction Methods: Intersections with All-Way Stop Control This section of the report describes the development of crash prediction models for all-way stopcontrolled intersections and presents the final models recommended for incorporation in the second edition of the HSM. Read the entire page →
From page 58... ... 58 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. Read the entire page →
From page 59... ... 59 intersection attributes collected, their definitions, and permitted values for all-way stopcontrolled intersections. Once all necessary data were entered into the data collection tool and saved for a given intersection, the data collection tool was used to validate the inputs for that particular intersection consistent with the range and/or permitted values for the respective variables/parameters. Read the entire page →
From page 60... ... 60 During detailed data collection, to the extent possible, the research team reviewed historical aerial images to determine if a site had recently been reconstructed or improved to determine which years of data should be used in model development. Crash and traffic volume data were obtained for California and Minnesota using HSIS databases. Read the entire page →
From page 61... ... 61 Crashes Of the 405 intersections included in the database, 70 (17%) experienced no crashes over the entire study period; their breakdown by area type and intersection type is as follows: • Rural three-leg intersections: 5 out of 12 • Rural four-leg intersections: 39 out of 199 • Urban three-leg intersections: 3 out of 33 • Urban four-leg intersections: 23 out of 161 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. Read the entire page →
From page 62... ... 62 Table 4. Major- and minor road AADTs and total AADT statistics by area type at all-way stop-controlled intersections Major Road AADT (veh/day) Read the entire page →
From page 63... ... 63 Table 5. All crashes combined and single- and MV crash counts by intersection type and crash severity -- rural all-way stop-controlled intersections State Date Range Number of Sites Number of Site-Years Time of Day All Crashes Combined SV Crashes a MV Crashes Total FI PDO Total FI PDO Total FI PDO RURAL THREE-LEG INTERSECTIONS IL 2008-2012 8 40 All 34 9 25 8 4 4 26 5 21 Night 11 4 7 6 3 3 5 1 4 OH 2009-2013 4 20 All 9 5 4 3 2 1 6 3 3 Night 5 3 2 3 2 1 2 1 1 All states 2008-2013 12 60 All 43 14 29 11 6 5 32 8 24 Night 16 7 9 9 5 4 7 2 5 RURAL FOUR-LEG INTERSECTIONS CA 2006-2011 29 174 All 252 77 175 26 4 22 226 73 153 Night 49 12 37 7 0 7 42 12 30 IL 2008-2012 87 435 All 405 99 306 42 14 28 363 85 278 Night 86 22 64 12 5 7 74 17 57 MN 2007-2011 17 85 All 55 22 33 12 6 6 43 16 27 Night 13 7 6 5 1 4 8 6 2 OH 2009-2013 66 327 All 279 75 204 48 13 35 231 62 169 Night 83 19 64 26 7 19 57 12 45 All states 2006-2013 199 1,021 All 991 273 718 128 37 91 863 236 627 Night 231 60 171 50 13 37 181 47 134 a Total and FI SV crashes include pedestrian and bicycle crashes. Read the entire page →
From page 64... ... 64 Table 6. All crashes combined, single- and MV, and pedestrian and bicycle crash counts by intersection type and crash severity -- urban all-way stopcontrolled 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 URBAN THREE-LEG INTERSECTIONS CA 2006-2011 5 30 All 18 9 9 10 6 4 8 3 5 0 0 Night 7 4 3 4 2 2 3 2 1 0 0 IL 2008-2012 17 85 All 83 21 62 8 2 6 71 15 56 3 1 Night 26 3 23 5 0 5 20 2 18 1 0 OH 2009-2013 11 55 All 78 16 62 22 5 17 55 10 45 0 1 Night 24 4 20 12 3 9 12 1 11 0 0 All States 2006-2013 33 170 All 179 46 133 40 13 27 134 28 106 3 2 Night 57 11 46 21 5 16 35 5 30 1 0 URBAN FOUR-LEG INTERSECTIONS CA 2006-2011 13 78 All 89 34 55 14 3 11 73 29 44 2 0 Night 16 5 11 7 1 6 9 4 5 0 0 IL 2008-2012 60 300 All 608 132 476 20 2 18 566 108 458 14 8 Night 127 33 94 5 0 5 118 29 89 4 0 MN 2007-2011 28 138 All 115 36 79 14 4 10 97 28 69 1 3 Night 22 5 17 7 2 5 15 3 12 0 0 NV 2007-2011 26 130 All 180 67 113 28 9 19 152 58 94 0 0 Night 67 30 37 16 6 10 51 24 27 0 0 OH 2009-2013 34 170 All 140 24 116 14 3 11 124 19 105 0 2 Night 36 7 29 4 1 3 32 6 26 0 0 All States 2006-2013 161 816 All 1132 293 839 90 21 69 1012 242 770 17 13 Night 268 80 188 39 10 29 225 66 159 4 0 Read the entire page →
From page 65... ... 65 Table 7. Crash counts by collision type and manner of collision and crash severity at rural all-way stopcontrolled intersections Rural Three-Leg Intersections Rural Four-Leg Intersections Total FI PDO Total FI PDO SINGLE-VEHICLE CRASHES Collision with animal 0 0 0 5 2 3 Collision with bicycle 0 0 0 4 4 0 Collision with pedestrian 0 0 0 1 1 0 Overturned 0 0 0 6 5 1 Other SV collision 11 6 5 112 25 87 Total SV crashes 11 6 5 128 37 91 MULTIPLE-VEHICLE CRASHES Angle collision 11 3 8 453 136 317 Head-on collision 0 0 0 14 4 10 Rear-end collision 18 5 13 289 81 208 Sideswipe collision 2 0 2 61 7 54 Other MV collision 1 0 1 46 8 38 Total MV crashes 32 8 24 863 236 627 Total Crashes 43 14 29 991 273 718 Table 8. Read the entire page →
From page 66... ... 66 Where: Nspf int = predicted average crash frequency for an intersection with base conditions (crashes/year) AADTmaj = AADT on the major road (veh/day) Read the entire page →
From page 67... ... 67 Based on these distributions, the following final modeling approach was chosen: • Rural three-leg intersections: Because of the small number of intersections, SPFs were developed using both lighted and unlighted intersections combined; total crashes at lighted intersections were adjusted in reverse using the CMF for lighting based on the work by Elvik and Vaa (2004) and shown in Equation 10-24 in Chapter 10 in the HSM (i.e., divide rather than multiply the crashes by the CMF) Read the entire page →
From page 68... ... 68 Table 9. SPF coefficients for intersections with all-way stop control on rural two-lane highways Intersection Type Parameter Estimate Standard Error Pr > F Significance Level TOTAL CRASHESa Three-Leg Intercept -9.05 3.28 -- -- ln(AADTtotal) Read the entire page →
From page 69... ... 69 Figure 6. Graphical representation of the SPF for total crashes at rural four-leg, all-way stop-controlled intersections Table 10. Read the entire page →
From page 70... ... 70 Table 11. Distributions for collision type and manner of collision and crash severity at rural all-way stopcontrolled intersections Collision Type Percentage of Total Crashes by Collision Type Rural Three-Leg All-Way Stop-Controlled Intersections Rural Four-Leg All-Way Stop-Controlled Intersections Total FI PDO Total FI PDO Single-Vehicle Crashes Collision with animal 0.0 0.0 0.0 0.5 0.7 0.4 Collision with bicycle 0.0 0.0 0.0 0.4 1.5 0.0 Collision with pedestrian 0.0 0.0 0.0 0.1 0.4 0.0 Overturned 0.0 0.0 0.0 0.6 1.8 0.1 Other SV collision 25.6 42.9 17.2 11.3 9.2 12.1 Total SV crashes 25.6 42.9 17.2 12.9 13.6 12.7 Multiple-Vehicle Crashes Angle collision 25.6 21.4 27.6 45.7 49.8 44.2 Head-on collision 0.0 0.0 0.0 1.4 1.5 1.4 Rear-end collision 41.9 35.7 44.8 29.2 29.7 29.0 Sideswipe collision 4.7 0.0 6.9 6.2 2.6 7.5 Other MV collision 2.3 0.0 3.4 4.6 2.9 5.3 Total MV crashes 74.4 57.1 82.8 87.1 86.4 87.3 Total Crashes 100.0 100.0 100.0 100.0 100.0 100.0 Table 12 shows the coefficients and associated statistics of the final SPFs for urban all-way stopcontrolled intersections. Read the entire page →
From page 71... ... 71 Figure 7. Graphical representation of the SPF for FI crashes at urban and suburban three-leg, all-way stopcontrolled intersections Figure 8. Read the entire page →
From page 72... ... 72 Figure 9. Graphical representation of the SPF for FI crashes at urban and suburban four-leg, all-way stopcontrolled intersections Figure 10. Read the entire page →
From page 73... ... 73 Table 13 (similar to Table 11 for rural intersections) provides percentages of total crashes by collision type and severity level for urban all-way stop-controlled intersections. Read the entire page →
From page 75... ... 75 which seems reasonable as the traffic control at all-way stop-controlled intersections provides more direction in terms of defining the right of way through the intersection for drivers so it is reasonable to expect fewer crashes at all-way stop-controlled intersections than intersections with minor road stop control, given the same traffic volumes. Although not presented herein, a similar trend was found in terms of the 3aST SPFs predicting fewer crashes than the 3ST SPFs in the HSM as the major road AADT increases for intersections on urban and suburban arterials. Read the entire page →
From page 76... ... 76 Figure 12. Comparison of new crash prediction model to existing model in HSM: 4aST vs 4ST on urban and suburban arterials (FI crashes) Read the entire page →
From page 77... ... 77 Thus, the only CMF recommended for use with the final SPFs for all-way stop-controlled intersections is the CMF for intersection lighting based on the work by Elvik and Vaa (2004) Read the entire page →
From page 78... ... 78 No traffic or geometric variables showed consistent and statistically significant effects in the SDFs for rural three-leg, rural four-leg, urban three-leg, or urban four-leg all-way stop-controlled intersections. Therefore, distributions for rural all-way stop-controlled intersections in Table 10 and SPFs by severity for urban all-way stop-controlled intersections in Table 12 are recommended for addressing severity at all-way stop-controlled intersections. Read the entire page →

From page 57...

... 57 Chapter 3. Development of Models for Use in HSM Crash Prediction Methods: Intersections with All-Way Stop Control This section of the report describes the development of crash prediction models for all-way stopcontrolled intersections and presents the final models recommended for incorporation in the second edition of the HSM.