Analysis of crash characteristics on freeways with depressed medians in Southcentral Alaska.
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2017-05-09
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Abstract:The characteristics of crashes on depressed medians of four freeways in Southcentral Alaska were examined under winter conditions. Cross-median crashes (CMC) were dispersed randomly along the freeways analyzed. CMC were 2.5 times likely to cause a severe injury crash compared to an in-median crash. Rollovers were 72.9%, a very high percentage, among all median crashes. Median slopes of 6H:1V (flatter) and 4:1/5:1 (steeper) were found to have similar frequency of cross-median and rollover crashes. On flatter slopes, higher frequency of non-rollover crashes was observed indicating reduced frequency of rollover crashes. With a median width of 32 ft (excluding inner shoulders), 54.7% of median crashes occurred. With a width of 36 ft, median crashes per mile were the highest for different crash types. As median width increased, in general, median crash frequency decreased. Two regression models were developed: a) Median rollover crashes were associated with severe injury crashes, driver inexperience, horizontal curves, median width between 26 and 40 ft, surface ice, and specific periods of the day, and b) CMC were associated with multiple vehicles, light trucks, after sunset on lighted roadways, and pavement rutting. Spatial analysis conducted identified nine top hotspots; five segments on New Seward Highway, three on Glenn Highway including location of median crashes, and one on Minnesota Drive. Six interchanges were identified for detailed examination.
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