5.2. SR 07-24-2000 - Laserfiche WebLink

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Synthesis of Safety Research Related to Speed and Speed Management - Turner-Fairbank.. Page 18 of' 25 Webster (1993) UK Speed humps Dahlerbrach (1993) USA Halbert et al. (1993) USA Bulpitt (1995) UK Speed humps Speed humps Humps and chicanes Gateway signing, Wheeler and Taylor (1995) UK marking, narrowing Webster and Mackie Mostly humps and speed (1996) UK tables Griffin and Reinhard Japan Chevron markings (1996) UK Transverse markings Ewing et al. (1998) US Speed humps Mini-circles 85th percentile speeds reduced 1 mi/h (16 km/h) Crashes reduced by 71% on treated streets Crashes reduced by 8% on surrounding roads Speeds reduced by 14% (5 mi/h) Traffic volume reduced by 7% 85th percentile speeds reduced by, 30% Traffic circles 85th percentile speeds reduced by 22% Speeds reduced by 10 mi/h (16 km/h) Crashes reduced up to 80% and traffic by 30 to 50% Speeds reduced 0-12 mi (0-19 km/h) Injury accidents decreased 14% Speeds reduced by 9 mi/h (14 km/h) Crashes reduced Crashes reduced Crashes reduced Crashes reduced by 22% Crashes reduced by 14% by 61 percent 25 to 50% 5 to 50% by 13%; speeds by 18%; speeds SUMMARY There is evidence that crash risk is lowest near the average speed of traffic and increases for vehicles traveling much faster or slower than average. The occurrence of a large number of crashes involving turning maneuver partly explains the increased risk for motorists traveling slower than average and confirms the importance of safety programs involving turn lanes, access control, grade separation, and other measures to reduce conflicts resulting from large differences in travel speeds. When the consequences of crashes are taken into account, the risk of being involved in an injury crash is lowest for vehicles that travel near the median speed or slower and increases exponentially for motorists traveling much faster. One of the major concerns in all of the studies is the travel speed before the crash. Emerging technology used in mayday, vehicle tracking, and adaptive speed control systems provide the opportunity to accurately and continuously capture travel speed. This technology should be applied in improving our understanding of the relationship between speed, speed variation, and safety. When a crash occurs, its severity depends on the change in speed of the vehicle at impact. The fatality risk increases with the change in speed to the fourth power. International research indicates the change in injury crashes will be twice the percentage change in speed squared, and fatal crashes will be four times the percentage change in speed. These relationships are based mainly on speed limit and speed changes on high-speed roads. More research is needed to assess their applicability to Iow-speed urban roads. In general, changing speed limits on Iow and moderate speed roads appears to have little or no effect on speed and thus little or no effect on crashes. This suggests that drivers travel at speeds they feel are reasonable and safe for the road and traffic regardless of the posted limit. However, http://www.ntl.bts.gov/ntl/DOCS/speed/speed.htm 07/19/2000