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原文传递 Safety Evaluation of Raised Speed Limits on Kansas Freeways, Technical Summary.

题名：	Safety Evaluation of Raised Speed Limits on Kansas Freeways, Technical Summary.
作者：	Dissanayake, S.; Shirazinejad, R.
关键词：	Speed limit, Safety evaluation, Crash contributory causes, Methodology
摘要：	Sections where the speed limit changed from 70 mph to 75 mph and other comparable sections where the speed limit remained at 70 mph without any change were identified. Details of the crashes by severity level for 3 years before (2008鈥?010) and 3 years after (2012鈥?014) the speed limit change were collected using the state crash database. In order to get a general understanding, characteristics of crashes such as nighttime versus daytime, number of trucks involved, weather conditions, driver鈥檚 gender, and other such factors were considered. Furthermore, several crash contributory causes were also investigated before and after the speed limit change. In order to evaluate the safety situation, three methods were utilized: (1) Empirical Bayes (EB) observational before-and-after studies; (2) Before-and-after method with comparison group; and (3) Cross-sectional method using the Negative Binomial (NB) regression model. The evaluation was conducted to see if the speed limit change has caused an increase in total crashes or fatal and injury crashes. In regard to speed analysis, the t-test was applied to see whether significant increases in the 85th percentile speed were observed between before-and-after conditions. Since the sample size was large, the Kolmogorov-Smirnov (K-S) test was also conducted to see if there was any difference between two sets of speed data distributions in the before period compared to the after period.
报告类型：	科技报告