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69 TABLE 29 Number of unsignalized median opening sites Median Median Median Median openings in openings with openings with opening original accident data Median openings with field data both accident type catalog available Primary Supplementary Total and field data URBAN ARTERIAL CORRIDORS Midblock 1a 12 10 0 7 7 7 1b 23 1 0 1 1 0 2b 149 145 8 12 20 20 2c 11 10 5 8 13 10 Three-leg 3a 44 34 1 10 11 11 3b 183 99 5 25 30 19 3c 4 4 0 2 2 2 4a 37 20 4 7 11 4 4b 1 0 0 0 0 0 Four-leg 5a 43 41 2 6 8 8 5b 164 106 4 26 30 17 6a 14 10 1 5 6 5 Subtotal 685 480 30 109 139 103 RURAL ARTERIAL CORRIDORS Midblock 1a 29 27 1 6 7 7 1b 6 6 0 0 0 0 2a 1 0 0 0 0 0 2c 1 0 0 0 0 0 Three-leg 3a 63 49 0 4 4 4 3b 24 22 0 0 0 0 3c 21 21 0 0 0 0 4a 2 1 0 0 0 0 Four-leg 5a 55 43 1 0 1 1 5b 20 19 0 0 0 0 5c 2 2 0 0 0 0 6a 1 1 0 0 0 0 Subtotal 225 191 2 10 12 12 TOTAL 910 671 32 119 151 115 Major-road rear-end collision--collision between a sists of the number of accidents involving either a U-turn or vehicle making either a U-turn or left-turn from the major left turn through the median opening per million vehicles road into the median opening and a following major- turning through the median opening. road through vehicle For urban arterial corridors, median opening accident rates Cross-street collision--any collision involving a vehi- are substantially lower for midblock median openings than cle from the cross street for median openings at three-leg and four-leg intersections. Other or unknown collision type--collision where the For example, the accident rate per million median opening intended vehicle movements are unknown movements (i.e., U-turn plus left-turn maneuvers) at a direc- tional midblock median opening is typically only about 14 percent of the median opening accident rate for a directional MEDIAN OPENING ACCIDENT RATES median opening at a three-leg intersection. At conventional three-leg median openings, the average median opening Table 35 presents total median opening accident rate by accident rate at median openings with two left-turn lanes median opening type. The median opening accident rate con- (Type 3c) is substantially higher than the average median

OCR for page 69
70 TABLE 30 Turning volumes at median openings Average Turning volume at median openings Number two-way (percentage of total Median of major-road (veh/day) (percentage of major road ADT) median opening ADT) a opening median ADT type openings (veh/day) U-turn Left turn Total U-turn Left turn Total U-turn Left turn URBAN ARTERIAL CORRIDORS Midblock 1a 7 13,161 2 0 2 0.01 0.00 0.01 100.00 0.00 2b 20 33,495 700 0 700 2.09 0.00 2.09 100.00 0.00 2c 10 30,231 977 0 977 3.23 0.00 3.23 100.00 0.00 Three-leg 3a 11 14,446 11 95 106 0.08 0.66 0.74 10.38 89.62 3b 19 32,760 248 187 435 0.76 0.57 1.33 57.01 42.99 3c 2 42,361 79 307 386 0.19 0.72 0.91 20.47 79.53 4a 4 31,366 138 680 818 0.44 2.17 2.61 16.87 83.13 Four-leg 5a 8 34,324 259 622 881 0.75 1.81 2.56 29.40 70.60 5b 17 40,096 285 533 818 0.71 1.33 2.04 34.84 65.16 6a 5 38,476 552 1,065 1,617 1.43 2.77 4.20 34.14 65.86 RURAL ARTERIAL CORRIDORS Midblock 1a 7 21,309 88 0 88 0.41 0.00 0.41 100.00 0.00 Three-leg 3a 4 27,448 374 404 778 1.36 1.47 2.83 48.07 51.93 Four-leg 5a 1 28,126 346 555 901 1.23 1.97 3.20 38.40 61.60 a Major-road and median-opening volumes for year 2002. TABLE 31 Median opening accident frequency by median opening type Number Median opening accident Median opening a Median 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 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. 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.