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1 CHAPTER 1 Introduction 1.1 Background community, highway designers are having difficulty determin- ing when and where to use various roadside safety devices. The Single-vehicle, ran-off-road crashes are a major cause of multiple-performance-level concept involves selecting a road- serious injuries and fatalities along our nation's highways. side safety feature to match the range of expected impact con- Approximately 12,000 motorists lose their lives each year as a ditions in the area where it is to be installed. Under this design result of these crashes. Most of the efforts to reduce this car- philosophy, roadside safety features are developed to meet one nage have been focused on designing more forgiving roadsides of several different performance levels or impact capacities. by removing or relocating hazards and designing better safety Lower capacity--and presumably less costly--safety devices features to mitigate the severity of those hazards that cannot be are installed at sites where the risks of high-energy impacts are removed or relocated. The fact that the total number of single- lower. Although the multiple-performance-level concept has vehicle, ran-off-road crashes has remained relatively stable and been largely embraced by the roadside safety community, a even declined in recent years while the number of vehicle miles significant amount of uncertainty remains regarding how per- traveled has increased steadily indicates that these efforts have formance levels should be defined and where the various been successful. performance-level designs should be installed. Detailed data The safety performance of roadside features is evaluated on ran-off-road crashes could provide a sound basis for deter- primarily through full-scale crash testing. The purpose of this mining appropriate performance levels for different classes of testing is to observe and evaluate the performance of safety highway included in the study. features under impact conditions that are either similar or Safety performance evaluation criteria, such as occupant more severe than those associated with real-world crashes impact velocity (OIV) and ridedown acceleration (RA), are resulting in serious injuries and fatalities. Important crash test used as surrogate measures of the risk of injury for vehicle parameters, such as impact speed and angle, point of impact, occupants during full-scale crash tests. OIV is a theoretical and vehicle orientation have been selected based on find- estimate of the speed at which the head of an unbelted occu- ings from limited studies of ran-off-road accidents (1, 2, 3). pant would strike the dash board. RA is calculated as the max- Although full-scale crash test data provides a small window imum 10 ms average vehicle acceleration measured after into the nature of ran-off-road crashes, it does not provide occupant impact occurs. These measures are intended as indi- sufficient data to identify the impact conditions associated cators of the risk that an occupant will be seriously injured with serious injury and fatal crashes. The research program during an impact with a roadside safety device. Unfortunately, described herein is undertaken primarily to identify appro- these measures of occupant risk have never been successfully priate impact conditions for use in full-scale crash testing linked to actual injuries. The difficulty associated with estab- guidelines. lishing this link is the lack of available data where both the However, knowledge of the characteristics of ran-off-road actual injuries and occupant risk measures can be determined. crashes has many more applications than just selecting impact Detailed accident investigations that provide calculations of conditions for full-scale crash testing guidelines. Many of the the occupant risk parameters and include crash injury infor- decisions related to design guidelines and policies could bene- mation should provide the basis for determining the merits of fit significantly by better information on the impact conditions the current safety performance evaluation procedures. of ran-off-road crashes. For example, while the concept of Another measure of occupant risk includes occupant com- multiple performance levels is embraced by the roadside safety partment deformation and intrusion. NCHRP Report 350 (4)