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This study investigates the technique used and forces applied on the latch plate and buckle during typical seat belt operation and driving conditions. These techniques and forces are relevant to whether the latch plate can be partially engaged with the buckle during typical operation and whether the latch plate will dislodge during vehicle operation. In addition to studying the insertion of the latch plate, we examined the tensile forces that are applied to the latch plate and buckle during typical, non-crash driving conditions, and how these forces compare to the performance requirements established by the National Highway Traffic Safety Administration (NHTSA) as part of Federal Motor Vehicle Safety Standards (FMVSS) 209. These tensile forces are important in understanding whether the latch plate is likely to dislodge from the buckle if it is in a position of partial engagement.

Accident investigators are often required to determine if an occupant was using a seat belt during a collision. Substantial research has been conducted on the types of physical evidence generated on a seat belt by occupant loading during a collision. However, very little research has been conducted concerning the characteristics of physical evidence that is created when an occupant uses their seat belt improperly. Case studies with misused seat belts were reviewed showing tell-tales of atypical or improper restraint usage. Occupants also experienced injuries consistent with greater excursion and contact with vehicle interior surfaces. To compare the physical evidence of properly and improperly used restraints, automotive frontal sled tests were conducted with matched pairs of anthropomorphic test devices (ATD) with seat belts used both correctly and incorrectly. When the seat belt was used improperly, distinctly different marks were observed.

In rollover accidents, physical evidence of seat belt usage is occasionally difficult to discern. Typically, if a seat belt is used by an occupant in an accident, various seat belt components will display characteristic marks in well-defined locations. These marks are known as “witness marks” or “occupant load marks.” Witness marks in a rollover accident may be faint in comparison to those caused by the occupant restraint forces in high-energy planar collisions. Additionally, in situations where a seat belt buckle is alleged to have unlatched early in a rollover accident, the lack of clear occupant load marks may in some cases be attributed to an alleged “buckle release” that occurred very early in the rollover sequence, so that the seat belt did not sustain loading while in a latched condition.

When an automotive seat belt buckle is believed to have released during a motor vehicle accident, it is typically attributed to one of several potential mechanisms, including inertial release, partial engagement, inadvertent contact, or structural overload. While the majority of literature in the past has focused on the topic of inertial release, little has been written on other release mechanisms. This review paper addresses automotive seat belt buckle release by inadvertent contact between the buckle pushbutton and some other object. This paper describes the conditions that must be satisfied for inadvertent contact to result in buckle release, including release force, direction, and pushbutton travel. We explain the role of occupant kinematics and the likelihood of contact between and occupant's hand or arm and the pushbutton. Occurrences of inadvertent contact in safety testing and a real world case study are presented.

Accident investigators are often required to determine if an occupant was wearing their seat belt during a collision. Previous studies have provided examples of physical evidence relied upon by investigators to determine if the seat belt assembly was subjected to occupant restraint loading. This paper examines the potential for clothing fibers to be permanently transferred to the seat belt webbing during a collision. To evaluate fabric transfer evidence as an indicator of restraint usage by an occupant during a collision, the following issues were examined: automotive seat belt webbing construction and behavior under load, fiber evidence found on the webbing in new and used conditions, and the transfer of different types of clothing fibers to webbing during full-scale sled testing.

Detailed investigations continually demonstrate that vehicle collision environments are extremely unlikely to produce accelerations of sufficient magnitude and duration to cause inertial release of seat belt buckles. Recently, it has been proposed that the dynamic response of an end-release buckle mounted to the vehicle structure via a metal strap or wire rope can amplify acceleration levels experienced at the floor of the vehicle by a factor of 10 or more, to levels that are high enough to cause inertial release. Experiments and modeling presented here confirm that accelerations may be amplified from the floor of the vehicle to the seat belt buckle, but not by more than a factor of 1.3, and only for acceleration pulse durations that are very short. Shock table testing of end-release seat belt buckles shows that, even with amplification, the resulting buckle accelerations are far below those required to cause inertial release, even at very low webbing tension.