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Synthesis of Safety Research Related to Speed and Speed Management - Turner-Fairbank.. Page 17 of' 25 Woonerf concept whereby cars and pedestrians share the same space, at one extreme, to relatively unintrusive lane striping at the other. In their review of this subject, Fildes and Lee (1993) make it clear that the many traffic calming techniques have the common objective of transferring the costs associated with excessive speed from unprotected road users (i.e., death and injury of pedestrians and cyclists) to vehicle drivers and their passengers (i.e., discomfort, risk, damage to vehicle, longer travel time). Westerman (1990) describes the approach as usually applying a "friction factor" to physically restrict a vehicle and force a motorist to slow down. In contrast to simple traffic signs, most traffic calming techniques are continuously reinforcing. That is, a motorist incurs a penalty when ever a traffic calming device is encountered at excessive speed. Few studies have been conducted of the type that could provide evidence to support the claims that traffic calming techniques reduce the incidence of motor vehicle injuries and fatalities. The hypothesis, however, is intuitively compelling and the rapidly-expanding literature on the topic is beginning to include a few for-mai evaluation studies that show clear, positive effects on measures of traffic safety. The Effects of Traffic Calming The current review found the most effective traffic calming measures to involve vertical shifts in the roadway, such as speed humps and speed tables. However, the effectiveness of these measures is dependent upon spacing. Greater reductions in vehicle speeds and crashes are achieved when combinations of measures are implemented and when traffic calming is implemented systematically over a wider area than a single neighborhood. Reductions in the incidence and severity of crashes of 50percent or more are frequently reported, as summarized in table 4. However, most traffic calming projects result in reductions in traffic volume and many of the safety studies do not take this diversion into account. It is possible the crashes may be migrating to other roads. Table 4. Summary of the effects of traffic calming measures Reference Zidel et al. (1986) Bowers(1986) Chua and Fisher (1991) Herrstedt (1992) Kjemtrop andHerrstedt (1992 ) Engel and Thomsen (1992) Vis et al. (1992) Country UK Germany Australia Netherlands Netherlands and France Measure Rumble strips Speed tables, narrowing, chicanes, gateways Various methods Various methods (staggerings, gateways) Various methods (humps, staggerings) Denmark Various methods (humps, staggerings) Humps, Netherlands staggerings, islands Results Mean speeds reduced by 40% No change in crash rate injuries reduced by 50% Crashes reduced by 50% Through traffic reduced by 35% Vehicle speeds reduced by 25% Vehicle speeds reduced 6 mi/h (10 km/h) Crashes reduced by 30 to 60% Speeds reduced by 7 mi/h (11 km/h) Injury rate reduced by 72% in calmed areas Injury rate increased by 96% on adjoining streets Speeds reduced by 20%; volumes reduced 5-30% Crashes reduced by 5%, injury crashes by 25% http://www.ntl.bts.gov/ntl/DOCS/speed/speed.htm 07/19/2000