Safety of U-Turns at Unsignalized Median Openings (2004) / Chapter Skim
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Pages 59-67
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From page 59... ...
Specifically, the distribution of unsignalized median openings by state, median opening type, posted speed limit, number of through lanes, presence of special left-turn treatment, shoulder type, median width and type, and level of U-turn activity are presented. The catalog consisted of 62 arterial corridors in seven states.
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From page 60... ...
The distribution of sites by state provided a good geographical diversity for accident and field studies. Median Opening Type Based on the classification of median opening types presented in Chapter 4, there are a total of 17 typical median opening design as follows: • 1a = Conventional midblock median opening without left-turn lanes • 1b = Conventional midblock median opening with leftturn lanes • 1c = Conventional midblock median opening with leftturn lanes and loons • 2a = Directional midblock median opening without leftturn lanes • 2b = Directional midblock median opening with leftturn lanes • 2c = Directional midblock median opening with leftturn lanes and loons • 3a = Conventional median opening without left-turn lanes at three-leg intersection • 3b = Conventional median opening with one left-turn lane at three-leg intersection • 3c = Conventional median opening with two left-turn lanes at three-leg intersection 60 • 3d = Conventional median opening with left-turn lanes and loons at three-leg intersection • 4a = Directional median opening for left turns from major road at three-leg intersection • 4b = Directional median opening for left turns onto major road at three-leg intersection • 5a = Conventional median opening without left-turn lanes at four-leg intersection • 5b = Conventional median opening with left-turn lanes at four-leg intersection • 6a = Directional median opening for left turns from major road at four-leg intersection • 7a = Midblock jughandle to the left for U-turn maneuvers • 7b = Midblock jughandle to the right for U-turn maneuvers Table 17 presents the frequency of unsignalized median openings by median opening type.
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From page 61... ...
Most of the median openings had paved shoulders. TABLE 18 Number of unsignalized median openings by state and median opening type Median opening type Posted speed limit Low speed (≤ 50 mph)
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From page 62... ...
62 Median Opening Types Included in Data Collection and Analysis Based on the catalog of median opening designs that are representative of what actually exists in the field, the following median opening designs were given highest priority in the accident and field studies: • Type 1a = Conventional midblock median opening without left-turn lanes • Type 1b = Conventional midblock median opening with left-turn lanes • Type 2b = Directional midblock median opening with left-turn lanes • Type 2c = Directional midblock median opening with left-turn lanes and loons • Type 3a = Conventional median opening without leftturn lanes at three-leg intersection • Type 3b = Conventional median opening with one leftturn lane at three-leg intersection • Type 3c = Conventional median opening with two leftturn lanes at three-leg intersection • Type 4a = Directional median opening for left turns from major road at three-leg intersection • Type 5a = Conventional median opening without leftturn lanes at four-leg intersection • Type 5b = Conventional median opening with left-turn lanes at four-leg intersection • Type 6a = Directional median opening for left turns from major road at four-leg intersection These median opening designs appeared to be most commonly used by highway agencies and/or were most promising in terms of safety performance. The preceding list includes median opening Type 2c, directional midblock median opening with left-turn lanes and loons.
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From page 63... ...
Table 24 presents the number of median openings, by median opening type and geographic region, at which turning movement counts were obtained, either from the videotapes or from supplemental manual counts. To supplement the information on individual median openings obtained during the catalog process, the following site characteristics were documented during the field observational studies: • Median opening dimensions (i.e., length and width)
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From page 64... ...
1 – 1 4 – 9 1 3 – 6 5 30 Total 2 1 22 14 3 30 2 9 5 31 6 125 TABLE 24 Number of median openings (by median opening type) in each geographic region at which turning movement counts were obtained
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From page 65... ...
U-turn and left-turn accidents are presented Number of accidents Percentage of total accidents Median opening type No. of median openings U-turn Left turn U-turn and left turn Total U-turn Left turn U-turn and left turn Midblock 1a 37 4 13 17 185 2.2 7.0 9.2 1b 7 0 6 6 73 0.0 8.2 8.2 2b 145 6 125 131 1,423 0.4 8.8 9.2 2c 10 2 3 5 82 2.4 3.7 6.1 Three-leg 3a 83 2 112 114 640 0.3 17.5 17.8 3b 121 26 253 279 1,367 1.9 18.5 20.4 3c 24 1 35 36 273 0.4 12.8 13.2 4a 21 2 49 51 418 0.5 11.7 12.2 Four-leg 5a 84 4 116 120 750 0.5 15.5 16.0 5b 125 27 458 485 2,044 1.3 22.4 23.7 6a 11 5 123 128 353 1.4 34.8 36.3 Number of accidents Percentage of total accidents Crossing type No.
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From page 66... ...
Analysis of Traffic Conflicts and Driver Behavior at Existing Median Openings The videotapes recorded during the field data collection effort were reviewed to document how drivers behave in making U-turns and left turns through unsignalized median openings. Approximately, 152 hours of videotapes from 26 urban sites were reviewed.
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From page 67... ...
For purposes of conducting a traffic conflict analysis, the seven types of undesirable driver behavior were grouped into three conflict types: • Conflict Type A: A vehicle turning from the major road into the median opening causes the following vehicle on the major road to brake. This conflict type includes the following undesirable driving behaviors: (1)
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