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Pages 18-28

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From page 18...
... Typically, SPFs are negative binomial regression models that are estimated using generalized linear modeling.
From page 19...
... In practice, it is very difficult to find sites that are similar to each other, and so regression models are typically used. The state of the art is to use negative binomial regression models where crash frequency is the dependent variable and the independent variables may include site characteristics including major and minor road AADT.
From page 20...
... It is important to note that the standard errors shown are ‘ideal' standard errors, and the Highway Safety Manual recommends that these standard errors be increased by a factor of 2.0 for Total Crashes Rear-end Angle Injury & Fatal Heavy Vehicle CMF 0.814# 0.792# 0.745# 0.820# 0.956 Standard Error 0.062 0.079 0.086 0.083 0.177 Note: #Statistically significant at the 0.05 level (based on the ideal standard errors reported in this table) Table 5.1.
From page 21...
... Instead, these data were used as part of a cross-sectional analysis employed to compare the safety performance of similar signalized intersections and roundabouts. The EB analysis was used to investigate the safety effects of converting signals to roundabouts, but the study was based Location Treatment Sites Colorado 3 1adirolF 3anaidnI Maryland 2 Michigan 2 New York 11 North Carolina 2 South Carolina 1 Vermont 1 Washington 2 82latoT Table 5.2.
From page 22...
... The CMFunction is applicable between a total intersection AADT of 5,300 and 43,000. Increasing the Change Interval Description of Treatment and Crash Types of Interest This analysis examined the safety impacts of modifying the change interval at signalized intersections.
From page 23...
... These data were combined with the reference sites and data from the treatment sites in a cross-sectional analysis to investigate the individual yellow and all red phases with respect to the ITE recommended practice. The EB analysis was used to investigate the safety effects of modifications to the total change interval with respect to the ITE recommended practice.
From page 24...
... Injury crashes were significantly reduced as a result of increasing the total change interval to be less than the ITE recommended practice. Rear-end crashes were significantly reduced as a result of increasing the total change interval to be greater than the ITE recommended practice.
From page 25...
... A reference group of untreated signalized intersections was identified to match the treatment sites based on site characteristics, including number of approaches, presence of left-turn lanes, and traffic volumes. Data from North Carolina In North Carolina, data were available for 19 four-leg intersections that experienced a change in left-turn phasing on at least one leg of the intersection.
From page 26...
... The following primary target crash types were considered: • Total intersection crashes; • Total left-turn crashes; and • Total left-turn crashes from the FYA treated approach (this crash type was examined in Washington and Oregon, but not in North Carolina)
From page 27...
... Results Crash Modification Factors are provided in Table 5.9 for total intersection crashes and total intersection left-turn crashes (the common crash type investigated in the 3 states)
From page 28...
... Intersections in the first group experienced reductions in total intersection crashes and total intersection left-turn crashes that were statistically significant at the 0.05 level. Intersections in the second group experienced a smaller reduction that was not statistically significant at the 0.05 level.


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