| Comments: | This CMF is for non-PDO incapacitating injury, non-incapacitating injury, and fatality crashes from Table 4.9 (p. 53). Since “possible injury” is not listed under crash severity in the CMF Clearinghouse, this CMF entry will have the same severities selected as ID 4010 which is for total non-PDO crashes (i.e., fatal, serious injury, and minor injury). The absence of “possible injury” from the crash severity list, therefore, may cause some confusion among Clearinghouse users. The CMF standard error was computed using the confidence interval given in Table 4.9 (p. 53): (CMF upper limit-CMF lower limit)/(2*1.96). The crash data consisted of records from 1998 to 2007 but excluded records from 2002 (p. 24). The study method was before-after with comparison group. Since this is not available on the list for study methodology, simple before-after was selected. The before and after sample sizes were computed using Table 4-5 (p. 48) which lists the annual crash frequency in the before and after periods and Table 3-4 (p. 36) which lists the duration of the before and after periods. The average ADT for the before and after period for each treatment site is given in Table 4-7 (p. 49); however, the overall average ADT for the treatment group is not provided. To compute the overall average ADT for the treatment group, a weighted average was taken using the treatment site average ADTs and the treatment site before and after period lengths listed in Table 3-4 (p. 36): 44*2200+60*1800+43*1800+60*2200+36*4600+60*5500+36*2600+60*3200/(44+60+43+60+36+60+36+60)=2996 |
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