Safety Evaluation of Permanent Raised Pavement Markers (2004) / Chapter Skim
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From page 33... ...
A more in-depth discussion of the results is presented in Chapter 5. Appendix A contains tables with the individual safety performance functions and annual factors developed during the analysis.
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. 4.2 DISAGGREGATE ANALYSIS METHODOLOGY Disaggregate analysis performed on nighttime crashes included both univariate exploratory analysis and formal multivariate modeling.
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Key findings are as follows: • Illinois shows significant increases in total crashes (9.1 percent) , daytime crashes (17.9 percent)
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are shown in bold. TABLE 4-1 Results of safety evaluation of two-lane roadways (nonintersection crashes)
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For example, at AADTs ranging between 15,000 and 20,000 on a roadway with a degree of curvature less than 3.5, a decrease in nighttime crashes of 24.3 percent following PRPM installation can be estimated from the model as noted above. At lower AADTs and sharper curvature, PRPMs can in fact be associated with an increase in crashes.
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The urban Interstate highways without PRPMs in Milwaukee County were all illuminated and had a lower posted speed limit (45 mph or 72 km/h) when compared with fourlane freeways (55 mph or 86 km/h)
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, daytime crashes (6.5 percent) , and wet weather crashes (5.4 percent)
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