Safety of U-Turns at Unsignalized Median Openings (2004) / Chapter Skim
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Pages 68-78
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From page 68... ...
The median opening volumes constitute a small percentage of the major road volumes, ranging from 0.0 to 4.2 percent. MEDIAN OPENING ACCIDENT FREQUENCIES Tables 31 through 33 present frequencies of total accidents, fatal and injury accidents, and PDO accidents, respectively, by median opening type.
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From page 69... ...
at a directional midblock median opening is typically only about 14 percent of the median opening accident rate for a directional median opening at a three-leg intersection. At conventional three-leg median openings, the average median opening accident rate at median openings with two left-turn lanes (Type 3c)
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From page 70... ...
Median opening accident frequency (per median opening per year) Median opening type Number of median openings U-turn Left-turn Total U-turn Left-turn Total URBAN ARTERIAL CORRIDORS Midblock 1a 7 1 0 1 0.029 0.000 0.029 2b 20 1 3 4 0.010 0.030 0.040 2c 10 2 3 5 0.040 0.060 0.100 Three-leg 3a 11 1 8 9 0.018 0.145 0.164 3b 19 5 27 32 0.055 0.297 0.352 3c 2 0 10 10 0.000 1.000 1.000 4a 4 0 7 7 0.000 0.304 0.304 Four-leg 5a 8 0 26 26 0.000 0.650 0.650 5b 17 5 71 76 0.056 0.798 0.854 6a 5 3 39 42 0.100 1.300 1.400 RURAL ARTERIAL CORRIDORS Midblock 1a 7 0 3 3 0.000 0.088 0.088 Three-leg 3a 4 0 4 4 0.000 0.235 0.235 Four-leg 5a 1 2 2 4 0.500 0.500 1.000 a The study period was generally five years in duration.
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From page 71... ...
The videotape recordings made during the field data collection effort were reviewed to document how drivers behave in making U-turns and left turns through unsignalized median openings. Three basic conflict types were observed and analyzed: • Conflict Type A: A vehicle turning from the major road into the median opening causes the following vehicle on the major road to brake.
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From page 72... ...
For example, the median opening accident rate at a directional midblock median opening is typically only about 14 percent of the median opening accident rate for a directional median opening at a three-leg intersection. • Median opening accident rates are slightly lower at conventional three-leg median openings than at conventional four-leg median openings.
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From page 73... ...
However, only four years of accident and exposure data were available for sites in New Jersey, and six years of accident and exposure data were available for sites in New York. TABLE 34 Collision type distribution for median opening turning accidents Median opening type Number of median openings Total median opening accident frequencya (for entire study period)
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From page 74... ...
For example, median opening accident rates are substantially lower for midblock median openings than for median openings at three- and four-leg intersections. This is not surprising given that midblock median openings do not have cross-street traffic turning through the median opening, thus creating additional points of conflict.
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From page 75... ...
TABLE 37 Property-damage-only median opening accident rate by median opening type Number of conflicts by conflict type Type Number of conflicts No. of conflicts per 103 majorroad vehicles Aa Bb Cc Midblock 2b 6 2.9 1 0 5 2c 36 20.6 0 1 35 Three-leg 3b 12 6.4 4 2 6 4a 43 34.1 6 0 37 Four-leg 5a 19 12.8 17 2 0 5b 31 10.2 7 5 19 6a 20 27.6 1 0 19 a Conflict Type A: Vehicle turning from the major road into the median opening causes following vehicle on the major road to brake.
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From page 76... ...
, which is about equal to the median opening accident rate for the conventional median opening. Comparison of Conventional and Directional Median Openings at Signalized Four-Leg Intersections Although the focus of the research was on unsignalized median openings, most of the directional midblock median openings in the study were sites in Michigan, where they are used in combination with signalized intersections.
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From page 77... ...
However, given that the median opening accident rate for directional midblock median openings is so low, it is likely that the safety performance of the directional median opening combination, as used in Michigan, is as good as or better than the safety performance of the conventional median opening.
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From page 78... ...
Signalized Four-Leg Intersection With No Turns Permitted and Two Directional Midblock Median Openings
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