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OCR for page 72
72 TABLE 33 Property-damage-only median opening accident frequency by median opening type Median opening accident Median opening a Median Number of frequency accident frequency opening median (for entire study period) (per median opening per year) type openings U-turn Left-turn Total U-turn Left-turn Total URBAN ARTERIAL CORRIDORS Midblock 1a 7 0 0 0 0.000 0.000 0.000 2b 20 0 1 1 0.000 0.010 0.010 2c 10 1 3 4 0.020 0.060 0.080 Three-leg 3a 11 0 5 5 0.000 0.091 0.091 3b 19 5 14 19 0.055 0.154 0.209 3c 2 0 4 4 0.000 0.400 0.400 4a 4 0 3 3 0.000 0.130 0.130 Four-leg 5a 8 0 16 16 0.000 0.400 0.400 5b 17 5 47 52 0.056 0.528 0.584 6a 5 1 14 15 0.033 0.467 0.500 RURAL ARTERIAL CORRIDORS Midblock 1a 7 0 1 1 0.000 0.029 0.029 Three-leg 3a 4 0 3 3 0.000 0.176 0.176 Four-leg 5a 1 2 2 4 0.500 0.500 1.000 a The study period was generally five years in duration. However, only four years of accident data were available for sites in New Jersey, and six years of accident data were available for sites in New York. Most traffic conflicts at midblock median openings and Median opening accident rates are substantially lower median openings at three-leg intersections, particularly for midblock median openings than for median open- directional median openings, were related to the turning ings at three- and four-leg intersections. For example, vehicle merging onto the major road from the median the median opening accident rate at a directional mid- opening (Conflict Type C). block median opening is typically only about 14 percent At median openings without left-turn lanes at four-leg of the median opening accident rate for a directional intersections, most of the traffic conflicts were related to median opening at a three-leg intersection. vehicles turning from the major road into the median Median opening accident rates are slightly lower at con- opening (Conflict Type A). ventional three-leg median openings than at conven- At directional median openings (Types 2b, 2c, 4a, and tional four-leg median openings. Median opening con- 6a), the greatest problem appears to be related to vehi- flict rates at conventional three-leg median openings are cles merging onto the major road from the median open- almost half the conflict rates at conventional four-leg ing, as evidenced by the large number of Type C traffic median openings. conflicts. Median opening accident rates at directional three-leg median openings are about 48 percent lower than the accident rates for conventional three-leg openings. In COMPARISON OF MEDIAN OPENING contrast, median opening conflict rates at directional ACCIDENT AND CONFLICT RATES three-leg median openings are substantially higher than the conflict rates for conventional three-leg openings. Table 39 presents median opening accident and conflict Median opening accident rates at directional four-leg rates by geometry type and number of intersection legs. All median openings are about 15 percent lower than for of the median openings are urban. Relative safety compar- conventional four-leg intersections. In contrast, median isons that can be made from the table include the following: opening conflict rates at directional four-leg median

OCR for page 72
73 TABLE 34 Collision type distribution for median opening turning accidents a Accident frequency by collision type Number (for entire study period) Percentage of accident frequency by collision type Median of Major- Major- Other Major opening median road road rear Cross or road Major-road Cross Other or type openings angle end street unknown Total angle rear end street unknown URBAN ARTERIAL CORRIDORS Midblock 1a 7 1 0 0 0 1 100.0 0.0 0.0 0.0 2b 20 2 2 0 0 4 50.0 50.0 0.0 0.0 2c 10 1 3 0 1 5 20.0 60.0 0.0 20.0 Three-leg 3a 11 0 4 4 1 9 0.0 44.4 44.4 11.1 3b 19 8 5 18 1 32 25.0 15.6 56.3 3.1 3c 2 9 1 0 0 10 90.0 10.0 0.0 0.0 4a 4 7 0 0 0 7 100.0 0.0 0.0 0.0 Four-leg 5a 8 16 8 2 0 26 61.5 30.8 7.7 0.0 5b 17 28 33 12 3 76 36.8 43.4 15.8 3.9 6a 5 35 2 3 2 42 83.3 4.8 7.1 4.8 RURAL ARTERIAL CORRIDORS Midblock 1a 7 0 2 1 0 3 0.0 66.7 33.3 0.0 Three-leg 3a 4 0 3 1 0 4 0.0 75.0 25.0 0.0 Four-leg 5a 1 1 2 1 0 4 25.0 50.0 25.0 0.0 a The duration of the study period was generally five years. 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 35 Total median opening accident rate by median opening type Total median opening Median opening accident Median opening accident rate a Median Number frequency movements (accidents per 6 6 opening of median (for entire study (10 turns during 10 turning type openings period) entire study period) vehicles) URBAN ARTERIAL CORRIDORS Midblock b b 1a 7 1 2b 20 4 17.20 0.23 2c 10 5 13.42 0.37 Three-leg 3a 11 9 2.23 4.04 3b 19 32 13.04 2.46 3c 2 10 1.20 8.35 4a 4 7 4.87 1.44 Four-leg 5a 8 26 11.16 2.33 5b 17 76 22.77 3.34 6a 5 42 16.36 2.57 RURAL ARTERIAL CORRIDORS Midblock 1a 7 3 0.96 3.13 Three-leg 3a 4 4 4.65 0.86 Four-leg 5a 1 4 1.41 2.84 a The duration of the study period was generally five years. 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. b Data too limited to be meaningful.