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Federal Highway Administration Research and Technology
Coordinating, Developing, and Delivering Highway Transportation Innovations
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This report is an archived publication and may contain dated technical, contact, and link information |
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Publication Number: FHWA-RD-98-133
Date: October 1998 |
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Accident Models for Two-Lane Rural Roads: Segment and Intersections6. Validation and Further AnalysisSummary Validation based on a chi-square statistic As assessed by the Log-Likelihood R-squared, the explanatory power of the highway variables is rather limited. Exposure and ADT account for about 27% of the variation. For the segments a total of 5.7% of the variation is accounted for by other highway variables (while STATE accounts for 2.6%). For the three-legged intersections, all highway variables other than ADT account for only 1.8% (perhaps in part because of the large overdispersion parameter in the three-legged model), while for the four-leggeds the other variables account for 2.1%. See Tables 46 and 47, and Figures 6 and 7. Although the cumulative scaled residual graphs for the segments suggest some differences in regimes, the graphs in Figures 8 through 15 are generally consistent with the model forms in Tables 27 and 35. Different models applied when some of the highway variables are confined to subsets of their full range (first quartile, second quartile, etc.) might yield better fits, but if a single overarching model is wanted for each of the three classes of data, the final models in Tables 27 and 35 are plausible candidates (with adjustments for different States and times).
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