[dcb]

There's a lot of good information in that link: Synthesis of Safety Research Related to Speed, Publication No. FHWA-RD-98-154

i.e. The relationship between impact speed and crash severity is particularly critical for pedestrians, the most vulnerable road users. In a recent review of the issues, the European Transport Safety Council (1995) report that only 5 percent of pedestrians died when struck by a vehicle traveling at 20 mi/h (32 km/h); however, the proportion of fatalities increased to 45 percent at 30 mi/h (48 km/h) and to 85 percent at 40 mi/h (64 km/h).

Of particular interest is table 3, where the vast majority of the studies indicate that a slower speed limit is safer

regarding changes in the speed limits worldwide:
"The results suggest that for every 1 mi/h change in speed, the number of injury crashes increases 5 percent or a 3-percent increase in injury crashes for every 1-km/h increase in speed."