Factors Contributing to Median Encroachments and Cross-Median Crashes (2014) / Chapter Skim
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6S E C T I O N 2 Past research on median safety has investigated the factors that caused vehicle encroachments, median crash frequency or severity, and countermeasures to prevent median encroachments. This section of the report summarizes the history of median safety research by reviewing past encroachment and crash studies, potential countermeasures, human factors research related to median encroachments, and scanning tours aimed at identifying median encroachment contributing factors.
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7 the traffic stream tend to position in the same vehicle path as those farther downstream. A 1980 study by Cooper (3)
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80.46 encroachments per MVMT was derived for winter weather conditions and attributed to the effect that pavement conditions have on driver behavior. The authors concluded that while there is a strong relationship between encroachments and ADT, Periods 1 through 3 are not recommended for consideration and that encroachments can be expected to increase during winter months.
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9 An investigation into the factors causing median encroachments and cross-median crashes was conducted by Sicking et al.
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10 However, Garner and Deen also stated that other median elements such as cross slopes and the presence of obstructions can have a greater effect on median crash experience than the median width. Garner and Deen (12)
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11 increments. As for the Illinois data, there is a sharp decline in relative effects between median widths in the range from 10 to 40 feet.
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12 roadway sections were expected to increase the median barrier crash frequency, holding all other variables constant. A unit increase in the median barrier offset was expected to decrease the median barrier crash frequency by 3.5 percent, holding all other variables constant.
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13 • Roadway friction factor if number of horizontal curves is greater than 0.67 per km (1.08 per mile) ; and • Section location (Interstate Route 90, Interstate Route 205, U.S.
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14 parameter estimates. The roadway inventory and traffic volume variables included in the models were as follows: • Median width (ft)
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15 • Posted speed limit (dummy variable for 60 mph, dummy variable for 65 mph, dummy variable for 70 mph)
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16 B/C ratio. Table 2-6 shows the calculated favorability ratios for various median widths and traffic volumes.
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17 ing the median; however, a collision with a vehicle traveling in the opposing travel lanes did not result. The crossover crash severity distribution was as follows: • Fatal: 6.5 percent (41 of 631)
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18 cost-effective in reducing severe CMC crashes. However, they increase the frequency of less severe fixed-object crashes.
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19 State/location Type of facility Type of collisions targeted Percent decrease (–) or percent increase (+)
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20 2.4 Road Safety Audits Agencies will occasionally conduct road safety audits (RSAs) to formally examine the safety performance of the highways within their jurisdictions.
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21 factors to the median-related crashes were rated by the RSA team. The specific factors were related to travel speeds, advanced warning of merging traffic, and guidance through the interchange in the middle of the study section.
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22 appropriate barrier type to use. The third was to determine which states have acceptance/rejection criteria for temporary concrete barriers used in work zones.
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