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This paper summarizes work relating to the assessment of societal benefits of side impact protection. National Crash Severity Study (NCSS) and National Accident Sampling System (NASS) accident data technigues were reviewed with respect to the reliability of output information concerning the distribution of side impact accidents by impact severity and relationships between injury and impact severity. NCSS and NASS are confounded by errors and inadequacies, primarily as a result of improper accident reconstruction based upon the CRASH computer program. Based on review of several sample cases, it is believed that the NCSS/NASS files underestimate Lower severities and overestimate higher severities in side impact, with delta-V errors probably overestimated by 25-30 percent in the case of the more serious accidents. These errors cannot be properly quantified except on a case-by-case basis. They introduce unknown biases into NCSS/NASS.

An understanding of fundamental kinematic relationships among the several deforming surfaces of side-impacting bullet and target vehicle, occupant protection system and occupant is fundamental to rational design of crash injury counter-measures. Unfortunately, such understanding is not easy to achieve. Side impacts address the full range of bodily contacts and injuries in a way that challenges analysis. Each bodily area and organ requires individual consideration for adequate injury protection. This paper presents a simplified graphical analysis of occupant kinematics and injury exposure applied specifically to the NHTSA-proposed crabbed moving deformable barrier (MDB) compartment impact, as described in NHTSA's Notice of Proposed Rulemaking (NPRM) for Federal Motor Vehicle Safety Standard (FMVSS) 214, issued in January of 1988 [NHTSA 1988 (1)*]. Projections are offered regarding the potential of thoracic injury counter-measures.

The original Malibu II study, conducted by Bahling et al, found that neck compression loading in rollover crashes is caused by the occupant moving toward the ground and therefore, roof crush was not causally related to the loading. Some have disputed this finding claiming that the occupant does not “dive toward the roof,” but rather, the roof “moves in” toward the occupant, and that roof deformation is the primary cause of cervical spine injuries in rollover crashes. The original study included a detailed analysis of film and force transducer data for 10 Potentially Injurious Impacts (PII's). This paper presents an independent analysis of these 10 PII's and one additional PII. This analysis uses the film and transducer data to evaluate the timing of roof deformation and neck loading, the magnitude of roof deformation at the time of peak neck load, and the motion of the vehicle and occupants in the inertial reference system.

Understanding of events within the history of a crash, and estimation of the severity of occupant interior collisions depend upon an accurate assessment of crash duration. Since this time duration is not measured independently in most crash test reports, it must usually be inferred from interpretations of acceleration data or from displacement data in high-speed film analysis. The significant physical effects related to the crash pulse are often essential in reconstruction analyses wherein the estimation of occupant interior “second collision” or airbag sensing issues are at issue. A simple relation is presented and examined which allows approximation of the approach phase and separation phase kinematics, including restitution and pulse width. Building upon previous work, this relation allows straightforward interpretation of test data from related publicly available test reports.

Heavier, larger pickups and SUVs are bound to encounter lighter, smaller passenger vehicles in many future accidents. As the fleet has evolved to include more and more SUVs, their frontal structures are often indistinguishable from pickup fronts. Improvements in geometric compatibility features are crucial to further injury prevention progress in side impact. In corner crashes where modern bullet passenger car (PC) bumpers make appropriate geometrical overlap with target PC rocker panels, concentrated loads sometimes disrupt foam and plastic bumper corners, creating aggressive edges. In situations where sliding occurs along the structural interface, these sharp edges may slice through doors, panels and pillars. End treatments for such bumper beams should be designed to reduce this aggressive potential.

A decade ago, James, et.al. published a detailed study of the available NASS data on severe rear impacts, with findings that “… stiffened or rigid seat backs will not substantially mitigate severe and fatal injuries in rear impacts.” No field accident study has since been advanced which refutes this finding. Advocates of rigidized seat backs often point to specific cases of severe rear impacts in which MAIS 4+ injuries are associated with seat back deformation, coupled with arguments supporting stiffer seatback designs. These arguments are generally based upon laboratory experiments with dummies in normal seating positions. Recent field accident data shows that generally, in collisions where the majority of societal harm is created, yielding seats continue to provide benefits, including those associated with whiplash associated disorders (WAD).

The BSAN crash pulse model has been shown to provide useful information for restraint sensing evaluation and for structural force-displacement studies in flat fixed rigid barrier (FFRB) crashes. This paper demonstrates a procedure by which the model may be extended for use with central and offset vehicle to vehicle (VTV) crashes through appropriate combinations of vehicle parameters.

Field experience has consistently indicated that lap-only belts and lap-shoulder belts perform well and about equally in prevention of fatalities and serious injuries in the rear seating positions. Analyses based on overall usage and injury figures from the Fatal Analysis Reporting System (FARS), double-pair analysis of FARS data, and still older data bases have shown that, in the rear outboard seating positions, injury rates are about the same for lap-only and lap-shoulder belted crash occupants. Although sparse, recently available field data from the 1988-2001 National Analysis Sampling System / Crashworthiness Data System (NASS/CDS) files confirm the finding that, when used by rear seat occupants, lap-only belts perform about equally with lap-shoulder belts as countermeasures for serious and fatal injury in severe frontal crashes.

Utilizing unembalmed cadaver test subjects, a series of tests was carried out to characterize quantitatively the resistance of the skin, the soft underlying tissue of the scalp, and certain other typical areas of the body to impact loading. The impacts were delivered by the use of an instrumented free-fall device similar to that previously employed for facial bone fracture experiments. In one group of tests, metal and glass edges were affixed to the impacting device to produce localized trauma under conditions which were standardized with respect to variables affecting the degree of the injury. In the second group of experiments, specimens of skin, together with underlying tissue of uniform thickness, were subjected to compressive impact between the parallel surfaces of the impacting weight and a heavy metal platen. From these latter experiments the force-time histories, coefficient of restitution, and hysteresis loops of load versus deflection were obtained for the specimens.

As part of a continuing study of thoracic injury resulting from blunt frontal loading, the interrelationship of velocity and chest compression was investigated in a series of animal experiments. Anesthetized male swine were suspended in their natural posture and subjected to midsternal, ventrodorsad impact. Twelve animals were struck at a velocity of 14.5 ± 0.9 m/s and experienced a controlled thoracic compression of either 15, 19, or 24%. Six others were impacted at 9.7 ± 1.3 m/s with a greater mean compression of 27%. For the 14.5 m/s exposures the severity of trauma increased with increasing compression, ranging from minor to fatal. Injuries included skeletal fractures, pulmonary contusions, and cardiovascular ruptures leading to tamponade and hemothorax. Serious cardiac arrhythmias also occurred, including one case of lethal ventricular fibrillation. The 9.7 m/s exposures produced mainly pulmonary contusion, ranging in severity from moderate to critical.

At the 1970 SAE International Automobile Safety Conference, the first experimental chest impact results from a new, continuing biomechanics research program were presented and compared with earlier studies performed elsewhere by one of the authors using a different technique. In this paper, additional work from the current program is documented. The general objective remains unchanged: To provide improved quantification of injury tolerance and thoracic mechanical response (force-time, deflection-time, and force-deflection relationships) for blunt sternal impact to the human cadaver. Fourteen additional unembalmed specimens of both sexes (ranging in age from 19-81 years, in weight from 117-180 lb, and in stature from 5 ft 1-1/2 in to 6 ft) have been exposed to midsternal, blunt impacts using a horizontal, elastic-cord propelled striker mass. Impact velocities were higher than those of the previous work, ranging from 14-32 mph.

Sternal and/or spinal acceleration data from eighteen of the unembalmed cadaver, blunt thoracic impact experiments reported by the authors at the Eighteenth Stapp Conference have been analyzed and several related response parameters computed. High acceleration levels, rates of onset, and Gadd Severity Indices were found in sternal acceleration measurements, whereas quite low values were obtained from the spinal regions in the same tests. A Severity Index value of 1000, computed from a sternal acceleration measurement, would be associated with only a mild exposure; whereas for a spinal measurement, the same value would reflect an extremely severe exposure. Correlation matrices which include cadaver characteristics, input and response parameters, and Abbreviated Injury Scale ratings show that none of the sternal acceleration parameters correlate well with AIS rating in the analyzed data base.

Previous studies of human thoracic injury tolerance and mechanical response to blunt, midsternal, anteroposterior impact loading were reported by the authors at the 1970 SAE International Automobile Safety Conference and at the Fifteenth Stapp Car Crash Conference. The present paper documents additional studies from this continuing research program and provides an expansion and refinement of the data base established by the earlier work. Twenty-three additional unembalmed cadavers were tested using basically the same equipment and procedures reported previously, but for which new combinations of impactor mass and velocity were used in addition to supplementing other data already presented. Specifically, the 43 lb/11 mph (19.5 kg/4.9m/s) and 51 lb/16 mph (23.1 kg/7.2 m/s) conditions were intercrossed and data obtained at 43 lb/16 mph (19.5 kg/7.2 m/s) and 51 lb/11 mph (23.1 kg/4.9 m/s).

One of the greatest challenges faced in the design of realistic occupant protection systems is an accurate statistical model of what is really needed. The paucity of data is this realm hinders designers of standards alike. Ideally, a model of crash statistics would correlate, for significant accident modes, injury level (as measured by AMA Abreviated Injury Scale “AIS”) with some adequate measure of crash intensity. Having this information, not only could the required level of safety design be ascertained, but also the justifiable economic expenditure could be estimated. This paper treats the statistical basis for deployment of a data retrival system. It provides a basis for estimates of the amount of data required, the number of vehicles to be instrumented, the crash severity trigger levels, and the economics of recorder installation, for various levels of injury and fatality.

The influence of body posture, and inherently support, on thoracic impact response was investigated in an animal model. Anesthetized and postmortem domestic swine were exposed to blunt, midsternal loading while supported in their natural quadrupedal posture, and the results were compared with previously reported data from similar tests involving an upright body orientation. Twelve male animals were tested, six while anesthetized and six postmortem. Each animal was impacted once by a 21 kg rigid mass with a flat contact interface moving at a nominal velocity of either 8 or 10 m/s. Measured mechanical responses included applied load, sternal and spinal accelerations, thoracic compression and aortic overpressure. Injury response was assessed from a thoracico-abdominal necropsy. In addition, ECG traces were recorded pre and postimpact to monitor electro-physiological response.

Far-side lateral impacts were simulated using a Part 572 dummy and human cadavers to compare responses for several belt restraint configurations. Sled tests were conducted having a velocity change of 35 km/hr at a 10 g deceleration level. It was estimated from field data that a 35 km/hr velocity change of the laterally struck vehicle represents about an 80th percentile level for injury-producing lateral collisions. Subjects restrained by a three-point belt system with an outboard anchored diagonal shoulder belt (i.e., positioned over the shoulder opposite the side of impact) rotated out of the shoulder belt and onto the seat. The subject received some lateral restraint due to interaction with the shoulder belt and seatback. The subjects restrained by a three-point belt system with an inboard anchored diagonal shoulder belt (i.e., positioned over the shoulder on the side of impact) remained essentially upright due to shoulder belt interaction with the neck and/or head.

Classical blunt thoracic impacts have involved midsternal anteroposterior loadings to an upright-positioned subject. Data on the sensitivity of human cadaver and/or animal model biomechanical and injury responses to blunt loadings at different sternal locations is needed to evaluate the efficacy of current injury-potential guidelines for nonsite-specific frontal impacts. In addition, the biomechanics and injury mechanisms associated with lateral impacts constitute a subject of increasing consideration for occupant protection. Twelve anesthetized pigs were subjected to various blunt frontal or a right-side impact to assess biomechanical and injury response differences in a living animal model.

The problem of occupant impact severity reduction by effective use of available space was studied using a two-degree-of-freedom linear mathematical model implemented on a digital computer. An optimum-search method was employed to find the best values of stiffness and damping terms for linear lap and shoulder “belts” corresponding to specific vehicle pulseforms and geometry at speeds 10 to 60 mph. System performance was evaluated on the basis of a severity index comparing occupant deceleration data, and upon penalties imposed for occupant contact with vehicle interior structures. Comparison to biomechanical data indicates that the optimal linear system for 60 mph could produce serious injuries. Comparison to theoretical optimum values indicates considerable room for improvement, using active or nonlinear passive systems.

The Simulation Model of Automobile Collisions (SMAC) computer program has seen more than a decade of use under NHTSA auspices. Although SMAC has proven itself to be a useful investigative tool, the program has several shortcomings which either have been addressed by the authors or need to be addressed by further work. This paper presents the results of our ongoing work to improve SMAC and our recommendations for further work. Those model features discussed herein which either have been or need to be revised consist of (1) the calculation of crush forces when penetration is deep (2) the representation of the vehicles' crush pressure vs deflection relationship and (3) the distribution of tire normal forces in reaction to pitch and roll. An input interfacing program called SMACED has been written and is discribed. This editing program greatly simplifies the use of SMAC and will be found particularly useful for the inexperienced or infrequent SMAC user.

This project covers one facet of a program to develop a mechanical model for characterizing the time history of local forces on the zygomatic, maxillary and mandible regions of the human face during a frontal collision. Two mechanical devices to measure the forces on crash dummies during testing were designed, constructed and tested. The devices employed cantilever beams equipped with strain gauges. Both devices were subjected to a series of drop tests onto various materials. Time histories were compared to those obtained from cadaver experiments. While the data obtained from this testing appears to be similar to the cadaver data, further improvements and modifications will make the model much more useful.