Accident Modification Factors for Traffic Engineering and ITS Improvements (2008) / Chapter Skim
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Pages 18-29
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From page 18... ...
; • Increasing pavement friction on intersection approaches (reanalysis of previous study data) ; and • Increasing pavement friction on roadway segments (reanalysis of previous study data)
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To accomplish this, the EB analysis requires beforetreatment and after-treatment crash and AADT data on the treatment sites and on a reference group of similar untreated sites. The similarity of untreated sites is determined on the basis of the geometrics of the sites (e.g., rural, four-leg, stopcontrolled intersections and non-intersection locations on urban, undivided, four-lane, non-freeways)
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The intersection types and the treatment and reference group sample sizes are noted in Table 5. Iowa data included a total of 19 treatment sites and 59 reference sites (three- and four-leg combined)
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. In the HSIS study, comparison sites were matched with treatment sites that were similar in terms of functional class, type of development, speed limit, intersection spacing, and access control.
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In addition, the "new" results use a much larger comparison group than the previous study, which used an equal number of treatment and comparison sites. Increasing Pavement Friction on Roadway Segments and at Intersection Approaches Description of Treatment and Crash Types of Interest This analysis examined the safety impacts of improving pavement skid resistance using data from the state of New York.
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Overall, dry road crashes showed a statistically significant 14-percent increase. However, this did not negate the effects on wet-road crashes, as shown by the statistically significant 20-percent decrease in total crashes when all intersection and crash types were combined.
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. Signalized Intersection Treatments in Urban Areas Description of Treatment and Crash Types of Interest This analysis examined the safety impacts of four urban safety treatments implemented at signalized intersections in Winston-Salem, North Carolina.
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of Treatment Sites Crash Type AMF(standard error) Replace permissive left-turn phasing with permissive/protected (1)
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Assuming that the overall severity of non-angle crashes is quite similar to that of rear-end crashes, the economic analysis revealed a reduction of about $11,800 per intersection-year in the overall crash harm due to this treatment. Replace Single Red Signal Head with Dual Red Signal Heads A second red signal head was added to the existing head at eight intersections in Winston-Salem.
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The analysis focused on total crashes and cross-median 27 Non-fatal Injury Crashes Fatal Injury Crashes 0v (mph)
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Here are the findings regarding the AMFs: • As expected, median width has a larger effect on crossmedian crashes than on total crashes; • The AMFs for cross-median crashes are very similar for the two urban roadway types with full access control (i.e., with four lanes and five or more lanes) ; • The AMFs for cross-median crashes are very similar for the two rural roadway types; and • The AMFs for total crashes are very similar for the two four-lane urban roadway types (with full access control and partial or no access control)
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From page 29... ...
Total Crashes Crossmedian Crashes Total Crashes Crossmedian Crashes 10 1.00 1.00 1.00 1.00 20 0.95 0.84 0.95 0.87 30 0.91 0.71 0.90 0.76 40 0.87 0.60 0.85 0.67 50 0.83 0.51 0.81 0.59 60 0.79 0.43 0.77 0.51 70 0.76 0.36 0.73 0.45 80 0.72 0.31 0.69 0.39 90 0.69 0.26 0.65 0.34 100 0.66 0.22 0.62 0.30 Table 15. AMFs for median width for roads with full access control.
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