COM 0649.004 2002-2004 - Laserfiche WebLink

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Also, the number of samples were categorized into four categories: o less than 20 mph (greater than 5 mph below the speed limit), 0 20 to 30 mph (within 5 mph of the speed limit), 0 31-35 mph (5-10 mph over the speed limit), and 0 over 35 mph (greater than 10 mph over the speed limit). The worksheets for the spot speed study before and after the sign installation, and uphill and downhill direction of travel, are included in the Appendix. A statistical analysis was conducted to determine whether any observed speed changes were statistically valid. A t-test was conducted between the "before" and "after" average speeds for each direction of travel. For this test, the null hypothesis tested was that there is no difference in the mean sample speeds at a 90% confidence level. The alternative hypothesis was that there is a difference. The null hypothesis was accepted if the calculated t -statistic was less than the t -statistic for the sample size and assumed confidence level. Otherwise, the alternative hpothesis was accepted. The formula for the t -statistic is: t = (Xa — Xb) — (Ua — Ubl Square Root {SP2 ((1/Na)-(1/Nb)]} where, t = calculated t -statistic, SP2 = _ (Na-1)Sa2 + (Nb-1)Sb2 the pooled variance, Na + Nb -2 Xa,Xb = mean sample after and before speeds, Ua,Ub = mean population after and before speeds, Na,Nb = Number of after and before samples, Sae, Sb2 = Variance of before and after means. D.3 Discussion with Kona Traffic Safety Committee Members of the Kona Traffic Safety Committee were contacted twice by email to obtain their opinions of the four way stop. The first contact was made in early September 2003 about a month after the implementation date to obtain initial opinions. A report summarizing the findings to date (but with no conclusions) 11.