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 6 of' 25 °.lt 10 20 30 40 50 G0 70 Change in speed ¢,V), mi/h Figure 5. Effect of change in speed ~ impact on fatality risk. 'crash traveling speeds were based on detailed investigations of each crash scene and computer-aided crash reconstruction. The average and median speed of traffic was about 60 km/h ( 37 mi/h). As shown in figure 6, the risk of being involved in an injury crash was lowest for vehicles traveling near or below the median speed and increased exponentially at higher speeds. Vehicles exceeding the 90th percentile speed or traveling more than 7 km/h faster (4 mi/h) than the speed limit and median speed had above average injury crash involvement rates. Nearly 25 percent of the cars involved in injury crashes were traveling faster than 72 km/h (45 mi/h) compared to only 2 percent of free flow traffic. Clearly, a research or engineering approach to speed management that ignores the injury consequences of vehicle speed could lead to unintended results. FACTORS INFLUENCING SPEED In most of the crashes involving a slow-speed vehicle, the operator of the slow-speed vehicle is either preparing for or in the process of a maneuver that required a slow speed for safe execution (e.g., turning, crossing, entering, or exiting). The current discussion focuses on the conditions in which driving speed is a matter of individual choice. Many different factors can influence the speed at which a motorist chooses to drive. Speed choice can be influenced by driver age, gender, attitude, and the perceived risks of law enforcement or crash. Speed choice also is influenced by situational factors, such as weather, road or vehicle characteristics, speed zoning, speed adaptation, impairment, or simply "running late." These and other factors are addressed in the following paragraphs. Driver Attitudes and Behavior Solomon (1964) identified the driver and vehicle characteristics associated with speeding on rural highways during the late 1950s. He reported higher mean speeds for young drivers, out of state vehicles, buses, and late model passenger vehicles, especially high-performance models. Other early studies linked driving speed to age, trip length, and presence or absence of passengers. More recently, Fildes et al. (1991) unobtrusively measured the speeds of vehicles on urban and 35 t ........................ [20 40 45 50 55 60 65 70 758 Travel speed, km/h Figure 6. Injury crash rural road segments in Victoria, Australia, then stopped a sample of the vehicles to interview the drivers. The researchers found that younger drivers, drivers without passengers, drivers of newer cars, drivers traveling for business purposes, and high mileage drivers were more likely to drive faster than average and exceed the speed limit. Mustyn and Sheppard (1980) found more than 75 percent of drivers claiming they drive at a speed that traffic and road conditions permit, regardless of the posted speed limit. Although the motorists who were interviewed tended to consider speeding to be one of the primary causes of crashes, they did not consider driving 10 mi/h (16 kin/h) over the limit to be particularly wrong. However, most of those interviewed considered driving 20 mi/h (32 kin/h) over the limit to be a serious offense. http://www.ntl.bts.gov/ntl/DOCS/speed/speed.htm 07/19/2000