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Synthesis of Safety Research Related to Speed and Speed Management - Turner-Fairbank.. Page 13 of' 25 Shinar and Stiebel (1986) demonstrated the relationship between perceived risk of receiving a citation and driving in excess of speed limits. The researchers found compliance with speed limits to be greatest in the vicinity of police vehicles and diminish with increasing distance; the distance halo effect was greater for mobile than stationary police vehicles. Benekohal et al. (1992) evaluated the impact of mobile patrol vehicle speed enforcement on car and truck speeds through a highway construction zone. They found that the presence of a marked patrol car reduced average car and truck speeds while no reduction o00urred in an unpatr011ed control condition. Additionally, the proportion of cars traveling faster than conditions permitted in the work zone was reduced by 14 percent, and trucks traveling faster by 32 percent, when the patrol car was present. A time halo effect on average truck speeds lasted for about I hour after patrols ended. Average car speeds increased immediately after patrols ended. In contrast, Vaa (1997) found that intensive enforcement (an average of 9 hours of police presence per day) resulted in reductions in vehicle speed that lasted up to 8 weeks. Stationary Patrol Vehicles Hauer et al. (1982) conducted several experiments to measure the impact of stationary patrol vehicle enforcement on traffic speeds before, at, and after the site of enforcement, and during and after the enforcement period (the time halo). The researchers detected a pronounced decrease in average traffic speed to the posted speed limit at the location of the patrol vehicle. By identifying vehicles passing through the enforcement area, the researchers also were able to determine that repeated exposure of the enforcement to drivers had no significant effect in speed reduction after the first encounter with the stationary patrol vehicle. Speeds returned to their pre- enforcement level within 3 days after a single dose of stationary enforcement whereas exposure to a stationary patrol vehicle over a 5-day period had the greatest effect in suppressing speeds after enforcement ended. Armour (1986) examined the impact on traffic speeds of parking a marked patrol car along an urban street. The presence of the patrol car was associated with (1) a 2/3 drop in the number of vehicles violating the speed limit; (2) an increase in community awareness of police enforcement in the surrounding area; and (3) a measurable decrease in speed at the site of enforcement. Based on these findings, Armour recommends the use of the stationary patrol car enforcement technique for localized speed problems. Stuster (1995) evaluated the effects of municipal speed enforcement programs on several dependent measures. Three communities were selected to participate in the study on the basis of comparability and isolation from each other. Two of the communities' police departments implemented special speed enforcement programs focused on six special enforcement zones within each community. Four of the zones in each community were selected on the basis of speed-involved crash statistics and two in each community on the basis of chronic citizen complaints of speeding. Police departments in the two experimental communities devoted an average of 8 hours of officer time each week td each of the zones. The department in the third community refrained from implementing any special traffic enforcement effort for the 6-month duration of the study. The study found significant declines in unobtrusive measures of vehicle speed and speed-related crashes in the special enforcement zones of the experimental communities. In addition, time series analyses found 112 fewer crashes than expected. Aerial Enforcement Research has demonstrated that aerial speed enforcement programs have a generally positive effect in reducing highway speeds. In western Australia, researchers compared the impact of changing the levels of aerial enforcement on several roadway sites maintaining aerial programs (Saunders, 1979). The removal of aerial enforcement in one site increased the percentage of cars violating the posted speed limit by 6.1 percent and the number of trucks by 6.2 percent. An increase in aerial enforcement at another site reduced the percentage of trucks violating the speed limit, but had no impact on the percentage of cars traveling above the limit. In a later Australian study, eleven months of aerial speed enforcement in New South Wales was investigated (Kearns and Webster, 1988). The aerial program resulted in a vehicle crash reduction of 22 percent. Blackburn, Moran and Glauz (1989) evaluated alternative methods of enforcing New York's then http://www.nd.bts.gov/ntl/DOCS/speed/speed.htm 07/19/2000