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Synthesis of Safety Research Related to Speed and Speed Management - Turner-Fairbank.. Page 12 o~" 25 <br /> <br /> USA 5-15 mi/h <br />Parker (1997) 22 states (3-24 km/h) <br /> <br />No significant changes <br /> <br />Based on the investigations of 50 separate speed limit changes on urban and rural roads in <br />Sweden, Nilsson (1981) derived a series of mathematical functions that explain the relationship <br />between changes in a speed limit and traffic safety. Figure 8 illustrates Nilsson's calculations, <br />which predict increases in fatal crashes as the change in vehicle velocity by a factor of 4, severe <br />injury crashes by a factor of 3, and all injury crashes by a factor of 2. <br /> <br />Based on the effects of speed limits reported in various international studies, Finch et al. (1994) <br />developed a model of the relationship between the change in mean speed and the change in <br />crashes. The results suggest that for every 1 mi/h change in speed, the number of injury crashes <br />increases 5 percent or a 3-percent increase in injury crashes for every 1 -km/h increase in speed. <br /> <br />ENFORCEMENT <br /> <br />The following paragraphs have been limited to summaries of quasi-experiments that have been <br />conducted to assess the effects of speed enforcement. <br /> <br />Mobile Patrol Vehicles <br />Raub (1985) reported on an Illinois State Police experiment in which the overhead lights on patrol <br />cars in an experimental group were removed. This group and a control group (more than 200 <br />cars in all) logged more than 5.5 million rural patrol miles in the course of the experiment. All <br />participating officers had similar driving records before the study was conducted. Officers driving <br />vehicles without roof-mounted lights improved their fuel mileage by 7 percent, were 25 percent <br />more productive in speed enforcement, and were involved in 65 percent fewer crashes. The <br />experiment lasted nearly two years and all results are statistically significant. Interestingly, while <br />the group without overhead lights was more productive in enforcing speed regulations, overall <br />productivity was not affected. <br /> <br />.15o~ - 10% -5% 0R 5% 10% t5% <br /> Change in speed <br /> <br /> Fi§ute 8. Efl.ects of changes in the speed on injury <br /> and fatal crashes ('from Nilsson, <br /> <br />http://www.ntl.bts.gov/ntl/DOCS/speed/speed.htm <br /> <br />07/19/2000 <br /> <br /> <br />