Improved Prediction Models for Crash Types and Crash Severities (2021) / Chapter Skim
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12 3 MODELS FOR TWO‐LANE RURAL HIGHWAYS 3.1 ROADWAY SEGMENTS Estimation and Validation Data To predict crash frequency and severity on two‐lane rural highways, the research team estimated and validated base condition SPFs for undivided roadway segments. To develop SPFs for undivided segments (2U) , we used segment crash and road characteristics data from Washington State (2008–12)
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13 Table 3‐2: Descriptive Statistics for Base Condition SPF Estimation, Two‐Lane Undivided (2U) Segments Variable WA (N = 361, 164.19 miles)
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14 Table 3‐3: Descriptive Statistics for Base Condition Validation Data, Two‐Lane Undivided (2U) Segments Variable Ohio (N = 321, 131.1 miles)
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15 Table 3‐4: Base Condition SPFs, Two‐Lane Undivided (2U) Segments Crash Type Washington (N = 361, 164.19 mi.)
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16 of observed same‐direction KA crashes is small, the calibration factor is the highest of all crash categories (3.848, compared to the second highest, 1.749, for SV KABCO) , and the calibration function fails to converge. In general, the models calibrate reasonably well for the Ohio data.
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17 Table 3‐5: Calibration and Validation of Washington SPFs Using Ohio Data, Two‐Lane Undivided (2U) Segments # Not significant at 90th percentile confidence interval. Crash Type Observed Crashes HSM Pred. MAD MSPE Calibration Factor (HSM)
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18 3.2 INTERSECTIONS Estimation and Validation Data SPFs for two‐lane rural highway intersections were estimated and validated using data collected from Minnesota and Ohio. The base conditions for three‐leg stop‐controlled (3ST) , four‐leg stop‐controlled (4ST)
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19 Table 3‐8 and Table summarize descriptive statistics for, respectively, the data used to develop models and the data used to validate them for base conditions at 3ST intersections, including the total number of crashes at all intersections. Table 3‐10 and Table 3‐11 present descriptive statistics for the data used to develop and validate models for base conditions at 4ST intersections. Table 3‐12 and Table 3‐13 show descriptive statistics for 4SG intersections. Table 3‐8: Descriptive Statistics for Base Condition SPFs, Two‐Lane Three‐Leg Stop‐Controlled (3ST) Intersections Variable Minnesota (N = 141)
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20 Table 3‐9: Descriptive Statistics for Base Condition Validation Data, Two‐Lane Three‐Leg Stop‐ Controlled (3ST) Intersections Variable Ohio (N = 2,081)
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21 Table 3‐10: Descriptive Statistics for Base Condition SPFs, Two‐Lane Four‐Leg Stop‐Controlled (4ST) Intersections Variable Minnesota (N = 198)
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22 Table 3‐11: Descriptive Statistics for Base Condition Validation Data, Two‐Lane Four‐Leg Stop‐ Controlled (4ST) Intersections Variable Ohio (N = 662)
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23 Table 3‐12: Descriptive Statistics for Modified Base Condition SPFs, Two‐Lane Four‐Leg Signal‐ Controlled (4SG) Intersections Variable Ohio (N = 202)
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24 Table 3‐13: Descriptive Statistics for Modified Base Condition Validation Data, Two‐Lane Four‐ Leg Signal‐Controlled (4SG) Intersections Variable Minnesota (N = 25)
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25 Estimated Models We first estimated base condition SPFs for all two‐lane rural intersections using NB modeling, as defined in Section 2. For some of these crash type–crash severity combinations, a dispersion factor of 0 was found; for those types, we show the Poisson modeling results as well. For some models, the parameter on AADT_min was not significant, so we estimated and show models for those crash types with total AADT instead. Following are the model forms used (as defined in Section 2)
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26 Table 3‐14: Base Condition SPFs, Two‐Lane Three‐Leg Stop‐Controlled (3ST) Intersections Crash Type Minnesota (N = 141)
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27 Table 3‐15: Base Condition SPF Using Poisson Distribution, Two‐Lane Three‐Leg Stop‐ Controlled (3ST) Intersections Crash Type Minnesota (N = 141)
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28 Table 3‐16: Base Condition SPFs, Two‐Lane Four‐Leg Stop‐Controlled (4ST) Intersections Crash Type Minnesota (N = 198)
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29 Table 3‐17: Base Condition SPFs Using Poisson Distribution, Two‐Lane Four‐Leg Stop‐ Controlled (4ST) Intersections Crash Type Minnesota (N = 198)
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30 Table 3‐18: Modified Base Condition SPFs, Two‐Lane Four‐Leg Signal‐Controlled (4SG) Intersections Crash Type Ohio (N = 202)
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31 Table 3‐19: Modified Base Condition SPFs Using Poisson Distribution, Two‐Lane Four‐Leg Signal‐Controlled (4SG) Intersections Crash Type Ohio (N = 202)
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32 Table 3‐20: Calibration and Validation of Minnesota SPFs Using Ohio Data, Three‐Leg Stop‐Controlled (3ST) Intersections *
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33 Table 3‐21: Calibration and Validation of Minnesota SPFs Using Ohio Data, Four‐Leg Stop‐Controlled (4ST) Intersections *
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34 Table 3‐22: Calibration and Validation of OH SPFs using MN Data (4SG)
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