Safety Prediction Models for Six-Lane and One-Way Urban and Suburban Arterials (2022) / Chapter Skim
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Pages 149-166
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149 CHAPTER 9. SEVERITY DISTRIBUTION FUNCTIONS This chapter describes the activities undertaken to calibrate SDFs for various components of the urban and suburban arterial system.
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150 jV = = + K k kjkj XbASC 1 , (225) where, jV = systematic component of crash severity likelihood for severity j.
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151 C = local calibration factor. The NLMIXED procedure in the SAS software was used for model calibration.
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152 Table 84. Crash SDF: six-or-more-lane arterials.
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153 I8D = indicator variable for eight-lane divided highway (= 1.0 if eight-lane divided, 0.0 otherwise)
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154 Road Type The effect of road type on crash severity was also considered in the calibrated model. About 55 percent of crashes occurred on six-lane divided roads, 16 percent occurred on eight-lane divided roads, and the remaining 29 percent occurred on six-lane undivided or six-lane with TWLTL segments.
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155 In addition to the variables included in the calibrated model, there may be differences between states, such as weather and driver behavior, that were not included in the model. Thus, indicator variables for the states of California, Oregon, and Illinois were included in the calibrated model to account for the overall differences between the states, which could not be explained with the variables included in the model.
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156 Table 89. Crash severity distribution of one-way segments based on lane width.
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157 Table 91. Crash severity distribution of one-way segments based on area type.
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158 Table 93. Crash SDF: two-way street signalized intersections.
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159 Iuturn = U-turn prohibition indicator variable (= 1.0 if prohibited, 0.0 if allowed)
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160 U-turn The U-turn prohibition variable indicates U-turn movement presence on the major street of a signalized intersection. About 27 percent of crashes occurred at intersections with U-turn prohibition.
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161 Table 98. Two-way street signalized intersection severity distribution based on lighting presence.
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162 The coefficients for Michigan and Illinois were relatively large and statistically significant. The negative sign of the coefficient for Michigan indicates that a crash at one-way street signalized intersections in Michigan is less likely to be classified as severe than a similar crash in Texas or California, when all other variables are controlled.
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163 Table 100. One-way street signalized intersection severity distribution based on area type.
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164 Table 102. One-way street signalized intersection severity distribution based on channelization.
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165 roadside design features, etc.) , terrain, weather pattern, driver behavior, and reporting accuracy for the various states.
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166 value of the associated coefficient (in Table 103) indicates that a crash occurring at a lighted intersection is likely to be less severe than a crash at an unlighted intersection, when all other variables are controlled.
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