Guidelines for Traversability of Roadside Slopes (2019) / Chapter Skim
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Pages 137-144
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From page 137... ...
B-1 A P P E N D I X B Risk Measures and Statistical Methods This appendix is intended as a more detailed technical description of the risk measures and statistical methods used in the crash data analysis to identify vehicle types that are more likely to roll over on slopes. The appendix is organized in following sub-sections: B.1 Risk Measures and Statistical Inferences B.2 Dealing with Crash Data Limitations B.3 Dealing with Sampling Errors in GES Data Mathematical notations used in this appendix are kept simple on purpose.
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From page 138... ...
B-2 Guidelines for Traversability of Roadside Slopes Total V j j rR 1 V j j nN 1 V j j V j j nrNRS 11 Vehicle CR is derived by dividing the proportion of a specific type of vehicles in passenger vehicles involved in slope-related rollover crashes by the proportion of the same type of vehicles in passenger vehicles involved in all slope-related crashes, which include both rollover and non-rollover crashes. It can be expressed mathematically as )
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From page 139... ...
Risk Measures and Statistical Methods B-3 An RR > 1 means the event (rollover on slopes) is more likely to occur in the study group than in the comparison group.
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From page 140... ...
B-4 Guidelines for Traversability of Roadside Slopes When vrR , i.e., when the number of slope-related rollover crashes for the non-Type v vehicle types is much larger than that of the Type v vehicle, the equation can be further reduced to 1 v)
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From page 141... ...
Risk Measures and Statistical Methods B-5 slope-related non-rollover crashes, vn , need to be estimable or at least estimable up to a constant, which is not the case with the crash data in consideration. Table B.2.
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From page 142... ...
B-6 Guidelines for Traversability of Roadside Slopes Using the same assumption and notation described in the last section, the standard error of the natural logarithm of the relative risk can be approximately estimated as follows: 1111 v)
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From page 143... ...
Risk Measures and Statistical Methods B-7 based data like GES data. Also, less sophisticated statistical methods usually assume the observations from individual sample cases are independent, which tend to understate the statistical uncertainty of estimates produced from such data.
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From page 144... ...
B-8 Guidelines for Traversability of Roadside Slopes )
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