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APPENDIX I STATISTICAL TESTING OF SPEED-BASED SAFETY MODELS Model 1 Dependent Variable APP Observations Used 36 Standard Wald 95% Confidence Chi- Parameter DF Estimate Error Limits Square Pr > ChiSq Intercept 1 -9.0059 3.7301 -16.3167 -1.6951 5.83 0.0158 logaadt 1 0.8255 0.4295 -0.0164 1.6674 3.69 0.0546 Speed_Differential_A 1 0.0622 0.0342 -0.0048 0.1291 3.31 0.0688 Dispersion 1 1.3683 0.6667 0.5265 3.5557 Model 2 Dependent Variable APP Observations Used 36 Standard Wald 95% Confidence Chi- Parameter DF Estimate Error Limits Square Pr > ChiSq Intercept 1 -9.9951 3.9006 -17.6402 -2.3499 6.57 0.0104 logaadt 1 0.8609 0.4307 0.0167 1.7050 3.99 0.0456 Approach_Speed__mph 1 0.0521 0.0286 -0.0040 0.1082 3.32 0.0686 Dispersion 1 1.3346 0.6678 0.5006 3.5586 NCHRP Web-Only Document 94: Appendixes to NCHRP Report 572: Roundabouts in the United States I-1
