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2 requires that "Deformations of, or intrusions into, the occu- roadside during a crash. Guardrail placement guidelines pant compartment that could cause serious injuries should also make recommendations regarding maximum flare rates. not be permitted." This requirement is relatively subjective Increasing the flare rate raises the vehicle impact angles and and has been interpreted differently by the various crash test- thereby increases crash severity. Detailed crash data, coupled ing agencies. The requirements are quantified under the Man- with injury severity information, should shed some light on ual on Assessment of Safety Hardware (MASH; 5) based on this relationship and thereby provide a better foundation for limited National Automotive Sampling System (NASS) data making recommendations on maximum flare rate. and engineering judgment. Nevertheless, a database with Finally, guidelines on grading requirements are provided for detailed information on ran-off-road crashes would provide guardrail terminals and crash cushions, including limits on the needed data to develop a link between the location and slopes in front of and behind these systems. These guidelines magnitude of vehicle intrusion and the severity of occupant are based mostly on data from limited full-scale crash tests injury. Any such link would provide an objective basis for without information from real-world crashes. Also, the RDG establishing limits on occupant compartment deformation provides guidelines as to roadside slopes that merit guardrail and intrusion. protection. Again, these guidelines are based on limited testing Vehicle stability is also used as a measure of occupant risk. and simulation. Detailed data on roadside topography for ran- Although crash data clearly shows that the risk of injury off-road crashes would provide additional insight into the cur- increases when a vehicle rolls over, some engineers believe rently accepted guidelines. that the risk of injury for occupants of vehicles that only roll 90 degrees is relatively low. Unfortunately, no data are avail- 1.2 Objective able that can be used to explore this possibility. If data on suf- The specific objectives for this study included the following: ficiently large numbers of ran-off-road crashes are collected, it may be possible to test this hypothesis. 1. Identify the vehicle types, impact conditions, and site char- Guidelines on the selection and placement of roadside safety acteristics associated with serious injury and fatal crashes features can also benefit from a detailed crash study such as the involving roadside features and safety devices; one described herein. Most current guidelines are based on 2. Create a robust relational database for future research; and benefit/cost analysis techniques and rely heavily on crash sever- 3. Develop an implementation plan for a long-term data col- ity estimates. These crash severity estimates are based on both lection effort. the estimated impact conditions, including speed, angle, and vehicle orientation at impact, as well as the severity resulting The first objective pertains to the collection of detailed infor- from any given impact condition. Data collected in this study mation on serious injury and fatal crashes involving roadside would be extremely valuable if collected in a sufficiently repre- features and safety devices. The data were then analyzed to sentative manner to allow an estimate of impact conditions identify the vehicle types, impact conditions, and site charac- associated with all ran-off-road crashes. Furthermore, if data teristics associated with these crashes. are collected in a representative manner, detailed crash recon- The second objective was to create a relational database suit- structions could also provide a wealth of crash severity data able for future research. The database consists of crash data with which to validate procedures for relating impact condi- from prior and current studies that have in-depth crash data tions to occupant risk. and will include future data collection efforts as well. Placement guidelines provide procedures for selecting and The third objective was to develop an implementation plan designing safety features to accommodate the characteristics of for a long-term data collection effort on detailed data for ran- specific sites. For example, guardrail installation guidelines rec- off-road crashes. As discussed previously, there are many addi- ommend procedures for calculating length-of-need and flare tional applications for such detailed crash data beyond the configurations based on the characteristics of the specific site current study, from performance evaluation of selected road- where the barrier is to be located. Many facets of safety hard- side safety features and devices to the formulation of policies ware installation guidelines are based on the expected vehicle regarding roadside safety. Thus, a long-term continuing effort trajectories and impact conditions at the given site. For exam- to collect detailed data on ran-off-road crashes would be highly ple, procedures for selecting guardrail runout lengths included desirable. in the Roadside Design Guide (RDG; 6) are based on vehicle trajectories measured in a study of encroachments into the 1.3 Scope medians of divided highways during the 1960s (7). Vehicle tra- jectory data collected in the current study should provide a sig- The scope of work for this study was specifically formu- nificant source of additional data regarding such information lated to address the three objectives and consisted of the fol- as the trajectories and the distances vehicles travel along the lowing major tasks: