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Among the several data recorded by a typical motor vehicle’s event data recorder (EDR) prior to, during and after a crash event, are sampled time histories of longitudinal and lateral components of delta-v. The delta-v components are not measured directly but are calculated by numerically integrating the outputs of two perpendicular accelerometers contained within the EDR box. As currently designed and implemented a typical EDR does not measure yaw velocity or track vehicle heading during the impulse phase of a crash. Without this yaw information to orient the accelerometers relative to the fixed ground, the delta-v values calculated by the EDR through direct integration of its measured acceleration components should not be interpreted as representing absolute changes in vehicle velocity, especially in cases where the yaw velocity is high. EDR-calculated delta-v components must be adjusted to account for the yaw motion that occurred during acquisition of the data.

Much has been written about reconstruction techniques and testing methods concerning vehicle rollovers. To date, most of the literature describes rollovers as one-dimensional events. Rollovers account for a disproportionate fraction of serious injuries and fatalities among all motor vehicle accidents. The three-dimensional nature of rollover sequences in which a rolling vehicle experiences multiple ground contacts contributes to the environment where such injuries occur. An analytical technique is developed to model the airborne segments of a rollover sequence as a parabolic path of the vehicle center of gravity. A formulation for the center of gravity descent from maximum elevation to full ground contact is developed. This formulation contains variables that may be readily determined from a thorough reconstruction. Ultimately, this formulation will also provide a vertical ground impact velocity at contact.

Most rollover literature is statistical in nature, focuses on reconstructed field data and experiences, or utilizes a very broad pool of dissimilar test data. When test data is presented, nearly all of it involves hard surface rollover tests performed at speeds near 30 mph, with a mix of passenger cars, sport utility vehicles and minivans. Five full-scale dolly rollover tests on dirt of production sport utility vehicles (SUV) and multi-purpose vehicles (MPV) were performed with similar input parameters. The similarities included Federal Motor Vehicle Safety Standard (FMVSS) 208 rollover dolly initiated events, level dirt rollover surfaces, and initiation speeds over 40 mph. All tests were recorded with multiple high-speed and real-time cameras. Additionally, some of the tests included detailed documentation of the rollover surface and the resulting evidence and debris patterns, as well as onboard angular rate sensing instrumentation.

Research focusing on automotive rollovers has garnered a great deal of attention in recent years. Substantial effort has been directed toward the evaluation of rollover resistance. Issues related to crashworthiness, such as roof strength and restraint performance, have also received a great deal of attention. Much less research effort has been directed toward a more detailed study of the rollover dynamics from point-of-trip to point-of-rest. The reconstruction of rollover crashes often requires a thorough examination of the events taking place between point-of-trip and point-of-rest. Increasing demands are placed on reconstructionists to provide greater levels of detail regarding the roll sequence. Examples include, but are not limited to, roll rates at the quarter-roll level, CG trajectory (horizontal and vertical), roll angle at impact, and ground contact velocity. Often the detail that can be provided in a rollover reconstruction is limited by a lack of physical evidence.

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.

In reconstruction of on-roadway vehicle accidents, tire-road surface friction coefficient, mu (μ), can be estimated using a variety of available data. Common ranges and values for μ are used in calculations forming the foundation for most accident reconstruction techniques. When the roadway surface is gouged or disrupted by vehicle components, accounting of dissipated energy can be successful where supporting force data exists. Roadway gouge forces can vary widely depending upon such factors as road surface construction, surface temperature, and the velocity and geometry of the gouging mechanism. Such dissipated energy can be significant in accounting of total reconstruction energy. This paper presents experiments aimed at quantifying gouge force by controlled pavement gouging tests.

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.

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.

The coefficient of restitution is an indicator of the elasticity of a collision. Restitution, or elastic rebound of a deformed surface, contributes to the change in velocity of collision partners, a common measure of injury severity in automobile collisions. Because of the complex nature of collisions between motor vehicles, the characterization of the expected magnitude of the coefficient in such collisions lacks detail and mechanisms influencing its value are not well understood. Using crash test data from the National Highway Traffic Safety Administration (NHTSA), this study investigates the expected magnitude of the coefficient of restitution and mechanisms influencing restitution in automobile collisions. Both vehicle-to-barrier and vehicle-to-vehicle tests are considered for all types of collisions. The influence of a variety of collision and vehicle parameters on restitution is also explored.

The reconstruction of accidental impacts to the side structure of one or more accident vehicles often incorporates estimates of the energy absorbed by laterally struck vehicle(s). Such estimates generally involve considerably more issues than does the assessment of frontal or rear impact deformation energy. The sides of vehicles are, compared to the usual striking object, relatively broad, and they contain zones of varying stiffness supported by collapsible box structures. Side stiffnesses can vary widely, depending upon impact geometry. Most side impact crash tests that can readily be used to make estimates of side stiffness have been conducted by the National Highway Traffic Safety Administration (NHTSA).

Occupant simulation models have been used to study trends or specific design changes in “typical” accident modes such as frontal, side, rear, and rollover. This paper explores the usage of the Articulated Total Body Program (ATB) as an accident reconstruction tool. The importance of model validation is discussed. Specific areas of concern such as the contact model, force-deflection data, occupant parameters, restraint system models, head/neck loadings, padding, and intrusion are discussed in the context of accident reconstruction.

Accident data suggest that a significant percentage of rear impacts involve occupants seated in other than a “Normal Seated Position”. Pre-impact acceleration due to steering, braking or a prior frontal impact may cause the driver to move away from the seat back prior to impact. Nevertheless, virtually all crash testing is conducted with dummies in the optimum “Normal Dummy Seated Position”. A series of 7 rear impact sled tests, having a nominal AV of 21 mph, with Hybrid III dummies positioned in the “Normal Dummy Seated Position”, “Out of Position” and slightly “Out of Position” is presented. Tests were performed on yielding production Toyota and Mercedes Benz seats as well as on a much stiffer modified Ford Aerostar seat. Available Hybrid III upper and lower neck as well as torso instrumentation was used to analyze and compare injury potential for each set of test parameters.

This paper presents a method of automobile collision analysis based on conservation of momentum. The analysis is applied to the collision of two two-dimensional bodies, either or both of which may be attached to a trailer. Newton's laws of motion are employed to determine changes in linear and angular velocities for the two-dimensional colliding bodies. Knowing the masses and rotational inertias and the initial velocities of all bodies at impact, the post-impact velocities can be calculated if appropriate constraints are applied to the bodies' post-collision motion. Various motion constraints, including lock-up, slip, and restitution are examined, and a methodology for modeling vehicle motion experienced during a collision is presented. The full set of basic equations characterizing this conservation-of-momentum analysis is presented with sufficient detail to allow their implementation on a programmable calculator or personal computer.

A controlled experiment involving road marks was conducted to compare various photogrammetry practices currently in use in the accident investigation community. The experimental controls and results are discussed for three variations of one 2-D scheme and for six 3-D photogrammetric schemes applied to a similar set of road marks and points. For measurements related to the most frequent issues in traffic accidents, all of the methods are capable of providing usable data. The experimental photographs and corresponding data represent a reference set for developing skills and for comparison with other photogrammetry schemes.

The National Highway Traffic Safety Administration (NHTSA) has recently opened a rulemaking docket seeking comments on the design of automobile seats and their performance in rear Impacts. There are two philosophies of seat design: one advocates rigid seats, the other advocates seats which yield in a controlled manner. A review of the legislative history of seat back design standards indicates that yielding seats have historically been considered a better approach for passenger cars. The design characteristics of current production automobile seats are evaluated and show no significant changes over the past three decades. Concerns about the performance of rigid seat backs in real world rear impacts are discussed, specifically increased injury exposure due to ramping, rebound and out-of-position occupants.

Recent cadaver studies have provided data for the development of force and stiffness characteristics of the side of the human head. A Hybrid III Anthropomorphic Test Dummy (ATD) head was modified to allow direct measurement of impact forces on the parietal and temporal regions by recasting the upper left half of the skull and installing triaxial piezoelectric force transducers. Dynamic impact tests of this modified head were conducted and force/stiffness characteristics for the temporal and parietal areas were compared to existing data on cadaver subjects. It was found that the existing Hybrid III vinyl skin satisfactorily represents the force/stiffness characteristics of the human head in these areas. This modified Hybrid III dummy head was also impacted against typical interior components likely to be contacted during a side impact. The force and acceleration test results are presented.

Recent detailed field accident data are examined with regard to injuries associated with rear impacts. The distribution of “Societal Harm” associated with various injury mechanisms is presented, and used to evaluate the performance of current seat back and restraint system designs. Deformation associated with seat back yield is shown to be beneficial in reducing overall Societal Harm in rear impacts. The Societal Harm associated with ejection and contact with the vehicle rear interior (the two injury mechanisms addressed by a rigid seat approach), is shown to be minimal. The field accident data also confirm that restraint usage in rear impacts has a substantial injury-reducing effect. Laboratory tests and computer simulations were run to investigate the mechanism by which seat belts protect occupants in rear impacts.

Impact tests were conducted on thirty-one unembalmed human cadaver heads. Impacts were delivered to the temporo-parietal region of fixed cadavers by two, different sized, flat-rigid impactors. Yield fracture force and stiffness data for this region of the head are presented. Impactor surfaces consisted of a 5 cm2 circular plate and a 52 cm2 rectangular plate. The average stiffness value observed using the circular impactor was 1800 N/mm, with an average bone-fracture-force level of 5000 N. Skull stiffness for the rectangular impactor was 4200 N/mm, and the average fracture-force level was 12,500 N.