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59 A p p e n d i x B The road departure crashes show different patterns of involve- ments than other crash types. Table B.1 shows the percentage distribution of selected environmental and driver conditions. The table shows distributions for road departure crashes (as defined hereâthat is, departing the road before a harmful event), nonroad departure crashes, and all crash types. The cells show the percentages, summing to 100% for each factor. Total involvements are shown at the bottom of the table. The percentages represent the 71,308 road departure involvements, 967,944 nonroad departure involvements, and 1,039,252 total involvements. Road departure crash involvements are more evenly dis- tributed across the week than are other crash involvements. If anything, they tend to be more prevalent on Saturday and Sunday, with some ramping up from the work week on Fri- day. Tuesday has the lowest incidence of road departure crash involvements. This pattern is in marked contrast with nonroad departure crash involvements, which tend to have a higher incidence in the work week (Monday through Friday), with a decline on Saturday and the lowest incidence on Sunday. Road departure crashes also show a relatively higher inci- dence of crash involvements in dark conditions, whether lighted or unlighted; on snowy or icy road surfaces; on roads in which access is fully controlled (such as Interstate high- ways); and in which the driver had been drinking or using illegal drugs. Road Departure Crashes by Environmental and Driver Conditions
60 Table B.1. Environmental and Driver Factors in Road Departure Crashes and Other Crash Types Factor Road Departure Crash? All Crash InvolvementsNo Yes Day of Week Sunday 9.2 16.1 9.6 Monday 14.8 13.7 14.8 Tuesday 15.2 12.5 15.0 Wednesday 15.6 13.8 15.5 Thursday 15.4 13.3 15.3 Friday 17.6 14.2 17.4 Saturday 12.1 16.5 12.4 Total 100.0 100.0 100.0 Light Condition Daylight 71.5 48.1 69.9 Dawn/dusk 5.1 5.5 5.1 Dark: Lighted 15.4 22.3 15.9 Dark: Unlighted 6.4 22.7 7.5 Other/unknown 1.6 1.2 1.6 Total 100.0 100.0 100.0 Road Surface Condition Dry 72.2 51.2 70.7 Wet 18.6 19.7 18.7 Icy 2.6 11.6 3.2 Snowy/slushy 4.2 14.5 4.9 Other/unknown 2.5 2.9 2.5 Total 100.0 100.0 100.0 Roadway Access Control No control 67.9 55.9 67.1 Full control 10.3 28.0 11.5 Other/partial 3.1 2.3 3.0 Unknown 18.7 13.9 18.4 Total 100.0 100.0 100.0 Alcohol Use None 97.4 88.3 96.8 Used 2.6 11.7 3.2 Total 100.0 100.0 100.0 Drug Use None 99.7 98.9 99.6 Used 0.3 1.1 0.4 Total 100.0 100.0 100.0 N = 967,944 71,308 1,039,252
