Appendixes to NCHRP Report 572: Roundabouts in the United States (2007)

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APPENDIX F STATISTICAL TESTING OF INTERSECTION-LEVEL SAFETY MODELS Total Collision SPF Definitions Of Independent Variables logaadt – log of the total entering AADT noappr 1 – 3 approaches 2 – 4 approaches 3 – 5 approaches nolanes 1 – 1 circulating lane 2 – 2 circulating lanes 3 – 3 or 4 circulating lanes Model 1 Observations Used 89 Standard Wald 95% Confidence Chi- Parameter DF Estimate Error Limits Square Pr > ChiSq Intercept 1 -3.6786 1.3235 -6.2726 -1.0845 7.72 0.0054 logaadt 1 0.5531 0.1394 0.2798 0.8264 15.74 <.0001 Dispersion 1 1.4986 0.2314 1.1073 2.0283 Model 2 Observations Used 87 Standard Wald 95% Confidence Chi- Parameter DF Estimate Error Limits Square Pr > ChiSq Intercept 1 -3.7075 2.3496 -8.3127 0.8976 2.49 0.1146 logaadt 1 0.7490 0.2197 0.3183 1.1797 11.62 0.0007 noappr 1 1 -1.4305 0.4750 -2.3614 -0.4997 9.07 0.0026 noappr 2 1 -0.6645 0.4033 -1.4550 0.1261 2.71 0.0995 noappr 3 0 0.0000 0.0000 0.0000 0.0000 . . nolanes 1 1 -1.6992 0.6054 -2.8859 -0.5126 7.88 0.0050 nolanes 2 1 -1.2070 0.6013 -2.3855 -0.0284 4.03 0.0447 nolanes 3 0 0.0000 0.0000 0.0000 0.0000 . . Dispersion 1 0.8986 0.1644 0.6278 1.2862 Model 3 Observations Used 52 Standard Wald 95% Confidence Chi- Parameter DF Estimate Error Limits Square Pr > ChiSq Intercept 1 -0.9397 3.1715 -7.1558 5.2764 0.09 0.7670 logaadt 1 0.5532 0.3007 -0.0362 1.1426 3.38 0.0658 noappr 1 1 -1.9545 0.6847 -3.2965 -0.6125 8.15 0.0043 noappr 2 1 -1.1971 0.6083 -2.3894 -0.0048 3.87 0.0491 noappr 3 0 0.0000 0.0000 0.0000 0.0000 . . nolanes 1 1 -2.3303 0.9895 -4.2696 -0.3910 5.55 0.0185 nolanes 2 1 -1.6670 0.9502 -3.5294 0.1954 3.08 0.0794 nolanes 3 0 0.0000 0.0000 0.0000 0.0000 . . newvar 1 0.1203 0.2768 -0.4222 0.6627 0.19 0.6639 Dispersion 1 0.8348 0.1965 0.5262 1.3242 NCHRP Web-Only Document 94: Appendixes to NCHRP Report 572: Roundabouts in the United States F-1

Model 4 Observations Used 58 Standard Wald 95% Confidence Chi- Parameter DF Estimate Error Limits Square Pr > ChiSq Intercept 1 0.1321 2.7914 -5.3390 5.6032 0.00 0.9623 logaadt 1 0.4162 0.2612 -0.0956 0.9281 2.54 0.1110 noappr 1 1 -1.7609 0.5917 -2.9207 -0.6012 8.86 0.0029 noappr 2 1 -1.0325 0.5037 -2.0198 -0.0452 4.20 0.0404 noappr 3 0 0.0000 0.0000 0.0000 0.0000 . . nolanes 1 1 -2.0821 0.8054 -3.6607 -0.5035 6.68 0.0097 nolanes 2 1 -1.3508 0.7954 -2.9097 0.2081 2.88 0.0894 nolanes 3 0 0.0000 0.0000 0.0000 0.0000 . . Inscribed_Diameter__ 1 0.0002 0.0021 -0.0039 0.0044 0.01 0.9147 Dispersion 1 0.7792 0.1746 0.5022 1.2088 Model 5 Observations Used 52 Standard Wald 95% Confidence Chi- Parameter DF Estimate Error Limits Square Pr > ChiSq Intercept 1 -0.7417 3.2568 -7.1249 5.6415 0.05 0.8199 logaadt 1 0.5597 0.3019 -0.0321 1.1515 3.44 0.0638 noappr 1 1 -1.9170 0.7194 -3.3269 -0.5071 7.10 0.0077 noappr 2 1 -1.1587 0.6228 -2.3794 0.0619 3.46 0.0628 noappr 3 0 0.0000 0.0000 0.0000 0.0000 . . nolanes 1 1 -2.3142 1.0454 -4.3632 -0.2652 4.90 0.0269 nolanes 2 1 -1.6943 0.9972 -3.6488 0.2602 2.89 0.0893 nolanes 3 0 0.0000 0.0000 0.0000 0.0000 . . Central_island_diame 1 -0.0006 0.0036 -0.0077 0.0065 0.03 0.8632 Dispersion 1 0.8408 0.1970 0.5311 1.3309 NCHRP Web-Only Document 94: Appendixes to NCHRP Report 572: Roundabouts in the United States F-2

Total Intersection - Fatal+Injury SPF Definitions Of Variables logaadt – log of the total entering AADT noappr 1 – 3 approaches 2 – 4 approaches 3 – 5 approaches nolanes 1 – 1 or 2 circulating lanes 3 – 3 or 4 circulating lanes Model 1 Observations Used 88 Analysis Of Parameter Estimates Standard Wald 95% Confidence Chi- Parameter DF Estimate Error Limits Square Pr > ChiSq Intercept 1 -7.8638 1.7497 -11.2931 -4.4345 20.20 <.0001 logaadt 1 0.7656 0.1825 0.4078 1.1233 17.59 <.0001 Dispersion 1 1.7262 0.4306 1.0587 2.8146 Model 2 Observations Used 86 Standard Wald 95% Confidence Chi- Parameter DF Estimate Error Limits Square Pr > ChiSq Intercept 1 -3.6232 2.8333 -9.1764 1.9299 1.64 0.2010 logaadt 1 0.5923 0.2531 0.0962 1.0885 5.48 0.0193 noappr 1 1 -1.2499 0.6354 -2.4953 -0.0044 3.87 0.0492 noappr 2 1 -0.8064 0.4739 -1.7352 0.1224 2.90 0.0888 noappr 3 0 0.0000 0.0000 0.0000 0.0000 . . nolanes 1 1 -2.2167 0.6467 -3.4843 -0.9491 11.75 0.0006 nolanes 3 0 0.0000 0.0000 0.0000 0.0000 . . Dispersion 1 0.9459 0.3294 0.4780 1.8718 Model 3 Observations Used 52 Standard Wald 95% Confidence Chi- Parameter DF Estimate Error Limits Square Pr > ChiSq Intercept 1 -0.4654 4.0732 -8.4487 7.5179 0.01 0.9090 logaadt 1 0.3637 0.3728 -0.3670 1.0943 0.95 0.3293 noappr 1 1 -2.0996 0.9457 -3.9532 -0.2460 4.93 0.0264 noappr 2 1 -1.5722 0.7938 -3.1279 -0.0164 3.92 0.0476 noappr 3 0 0.0000 0.0000 0.0000 0.0000 . . nolanes 1 1 -2.8410 1.0195 -4.8391 -0.8429 7.77 0.0053 nolanes 3 0 0.0000 0.0000 0.0000 0.0000 . . newvar 1 0.1249 0.3954 -0.6501 0.9000 0.10 0.7520 Dispersion 1 0.8714 0.4393 0.3244 2.3408 NCHRP Web-Only Document 94: Appendixes to NCHRP Report 572: Roundabouts in the United States F-3

Model 4 Observations Used 58 Standard Wald 95% Confidence Chi- Parameter DF Estimate Error Limits Square Pr > ChiSq Intercept 1 -1.5264 3.3073 -8.0086 4.9559 0.21 0.6444 logaadt 1 0.3971 0.3086 -0.2078 1.0020 1.66 0.1982 noappr 1 1 -1.6696 0.7076 -3.0564 -0.2828 5.57 0.0183 noappr 2 1 -1.4571 0.5681 -2.5705 -0.3437 6.58 0.0103 noappr 3 0 0.0000 0.0000 0.0000 0.0000 . . nolanes 1 1 -2.1759 0.9231 -3.9852 -0.3666 5.56 0.0184 nolanes 3 0 0.0000 0.0000 0.0000 0.0000 . . Inscribed_Diameter__ 1 0.0023 0.0031 -0.0038 0.0083 0.53 0.4663 Dispersion 1 0.6891 0.3561 0.2503 1.8975 Model 5 Observations Used 52 Standard Wald 95% Confidence Chi- Parameter DF Estimate Error Limits Square Pr > ChiSq Intercept 1 0.0335 3.9708 -7.7491 7.8161 0.00 0.9933 logaadt 1 0.3976 0.3854 -0.3578 1.1530 1.06 0.3023 noappr 1 1 -2.1836 0.9806 -4.1056 -0.2616 4.96 0.0260 noappr 2 1 -1.6783 0.8607 -3.3652 0.0087 3.80 0.0512 noappr 3 0 0.0000 0.0000 0.0000 0.0000 . . nolanes 1 1 -3.0939 1.1842 -5.4150 -0.7728 6.83 0.0090 nolanes 3 0 0.0000 0.0000 0.0000 0.0000 . . Central_island_diame 1 -0.0032 0.0065 -0.0160 0.0095 0.25 0.6205 Dispersion 1 0.8894 0.4447 0.3338 2.3697 NCHRP Web-Only Document 94: Appendixes to NCHRP Report 572: Roundabouts in the United States F-4