Research Article
Random-Parameter Multivariate Negative Binomial Regression for Modeling Impacts of Contributing Factors on the Crash Frequency by Crash Types
Table 8
Independent Poisson model estimation results.
| | Variables1 | No.2 | Rear-end estimate (t-stat) | Bumping-guardrail estimate (t-stat) | Other estimate (t-stat) | Noncasualty estimate (t-stat) | Casualty estimate (t-stat) |
| | Constant | 5 | 0.177 (1.41) | 0.515 (3.27) | −0.460 (−2.31) | 0.228 (2.51) | −0.348 (−1.07) |
| | Traffic characteristics | | Interchange | 3 | —3 | — | −0.3482 (−3.01) | −0.088 (−1.93) | −0.529 (−2.54) | | Black spots | 5 | 1.020 (16.68) | 0.859 (10.40) | 1.227 (10.68) | 1.083 (23.20) | 1.316 (6.10) | | AADT | 5 | 0.0000236 (10.04) | 0.00000909 (3.03) | 0.000011 (2.77) | 0.0000312 (18.14) | −0.000014 (0.047) |
| | Speed characteristics | | 5 | −0.0134 (−5.96) | −0.00807 (−2.81) | −0.0144 (−3.73) | −0.0181 (−10.98) | −0.0154 (−2.05) | | 5 | 0.0119 (5.27) | 0.00829 (2.85) | 0.0112 (2.80) | 0.0124 (7.53) | 0.0219 (2.70) | | 2 | 0.0209 (4.86) | — | — | 0.0285 (8.90) | — | | 4 | −0.0196 (−6.81) | −0.00939 (−2.54) | −0.0190 (−3.90) | −0.0234 (−11.05) | — |
| | Geometric characteristics | | 2 | 0.000000154 (2.54) | — | — | 0.000000148 (3.36) | — | | 3 | — | — | — | 0.0000506 (1.94) | 0.000272 (2.62) | | 2 | 0.000000410 (6.12) | — | — | 0.000000375 (7.71) | — | | 5 | 0.000567 (15.62) | 0.000460 (9.02) | 0.000659 (10.59) | 0.000630 (24.12) | 0.00075 (7.16) | | 1 | — | −0.000131 (−2.71) | — | — | — | | 1 | — | — | — | −0.108 (−2.44) | — | | 4 | −0.0003483 (−3.67) | — | −0.0004866 (−2.91) | −0.000437 (−6.18) | −0.000644 (−2.12) |
| | Sight characteristics | | 5 | −0.00644 (−4.78) | −0.00641 (−3.35) | −0.0118 (−4.28) | −0.00847 (−8.14) | −0.0142 (−3.03) | | 4 | −0.104 (−3.93) | −0.106 (−3.06) | −0.110 (−2.37) | −0.1232 (−6.11) | — |
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Total number of parameters: 61; log-likelihood: −16595.848; AIC: 33441.697; BIC: 33934.501; :50507.432. |
