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Synthesis of Safety Research Related to Speed and Speed Management - Turner-Fairbank.. Page 5 of' 25 The relationship between travel speed and the severity of injuries sustained in a crash was examined by Solomon (1964), who reported an increase in crash severity with increasing vehicle speeds on rural roads. From an analysis of 10,000 crashes, Solomon concluded that crash severity increased rapidly at speeds in excess of 60 mi/h (96 kin/h), and the probability of fatal injuries increased sharply above 70 mi/h (112 km/h). Bowie and Waltz (1994), in an analysis of tow-away crashes reported in the National Accident Sampling System over a 7-year period, found that the chance of being injured in a crash depended on the change in speed at impact (DV). As shown in table 1, the risk of a moderate or more serious injury was less than 5 percent when DV was less than 10 mi/h (16 km/h) and increased to more than 50 percent when DV exceeds 30 mi/h (48 km/h). Table 1. Injuries per 100 Occupants by Change in Speed (DV) at Impact Moderate Injury Serious Injury deltaV AlS 2+ AlS 3+ mi/h NCSS NASS NCSS NASS 1-10 2.4 4.5 0.7 1.0 11-20 9.5 10.6 3.5 2.6 21-30 25.3 29.2 13.9 11.1 31-40 51.8 53.4 37.2 27.9 41-50 70.3 67.2 58.3 40.6 50+ 64.7 69.3 56.9 54.3 1 mi/h = 1.61 km/h Joksch (1993) found that the risk of a car driver being killed in a crash increased with the change in speed to the fourth power as shown in figure 5. The risk of a fatality begins to rise when the change in speed at moment of impact exceeds 30 mi/h (48 km/h) and is more than 50 percent likely to be fatal when DV exceeds 60 mi/h (96 km/h). The probability of death from an impact speed of 50 mi/h (80 km/h) is 15 times the probability of death from an impact speed of 25 mi/h (40 kin/h). The fatality risk curve from an earlier study by O'Day and Flora (1982) is also shown for comparison. The shift in the curve to the right can be explained in part by improvements in vehicle crashworthiness, seat-belt use, and emergency medical care over time. (See TRB, 184; Evans, 1991; Zador and Ciccone,1991; and FORS, 1992). Probability of Fatality ]'The relationship between impact speed and crash severity is particularly critical for ,,4 pedestrians, the most vulnerable road users. y =(x In a recent review of the issues, the European Transport Safety Council (1995) report that --- Joksch, 1993 ,only 5 percent of pedestrians died when ~ O'Day and Flora, 1982 jfl struck by a vehicle traveling at 20 mi/h (32 km/h); however, the proportion of fatalities ncreased to 45 percent at 30 mi/h (48 kin/h) and to 85 percent at 40 mi/h (64 km/h). /~ I Kloeden et al. (1997) compared the estimated speeds of over 150 cars involved in non- alcohol related injury crashes in 60 km/h speed zones in Australia with the free speed of cars measured at the same location at the same time of day and day of week. The pre- http://www.ntl.bts.gov/ntl/DOCS/speed/speed.htm 07/19/2000