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Synthesis of Safety Research Related to Speed and Speed Management - Turner-Fairbank.. Page 9 of' 25 Fildes and Lee (1993) describe procedures for identifying appropriate speed limits in Australia that are remarkably similar to the methods followed in the United States. In general compliance with speed limits is poor. Harkey et al. (1990) found that 70 percent of the vehicles exceeded the speed limit on a representative sample of Iow and moderate speed roads in four States. Similar results are reported abroad by the European Transport Safety Council (1995). A number of studies have examined the effects of altering speed limits on speeds. Spitz (1984) reported that the 85th percentile speed of traffic increased less than 0.4 mi/h (0.6 km/h) in 40 zones where speed limits were raised in 10 California cities. This was less than the 0.7-mi/h (1.1- km/h) increase observed in the comparison sites which had no speed limit change. For the 10 zones where speed limits were lowered, speeds actually increased on average by 1.1 mi/h (1 .Skm/h). Dudek and Ulman (1986) found no significant changes in speeds at six sites in the urban fringe where speed limits were lowered from 55 to 45 mi/h (89 to 72 mi/h). Parker (1997), taking advantage of routine speed zoning changes being made by State and local agencies, evaluated the effects of raising and lowering speed limits by various amounts at 98 non-freeway sites in 22 States. Free-flow speeds were measured for a 24-hr period before the speed limit was altered and on the same day of the week about one year later. Before and after speeds were measured simultaneously at comparison sites where speed limits were not altered to control for time trends. As shown in figure 7, raising and lowering speed limits had little or no effect on speeds. Although maximum speed changes up to 3 mi/h (5 km/h) were observed at iridividual sites, the average change in the mean and 85th percentile speeds was less than I mi/h and similar to sites that were not changed. However, studies in the USA and abroad generally show an increase in speeds when speed limits are raised on freeways. Changes in mean speeds ranging from 1 to 4 mi/h were observed when the speed limits in the United States were increased from 55 mi/h (89 km/h) to 65 mi/h (105 km/h) as shown in table 2. Change in 85th Percentile Speed, mi~h I nor ea$e -15 &-20 -10 -5 +5 +10 &+l. Change in Posted Speed Limit, miSh I rnith= 1.61 krrv'h Figure 7. Effects of altering speed limits by various amounts on non-freeways (Parker, 1997). http://www.ntl.bts.gov/ntl/DOCS/speed/speed'htm 07/19/2000