Frontal Impact Rear Seatbelt Load Marks: An In-Depth Analysis

Forensic evidence left behind in the form of markings on the seatbelt system can reveal details of how the belt system was being used and how it performed in a collision. Information about how belt systems are being used and how they perform in the field is useful to the design engineer, but interpreting this forensic evidence can be very difficult. Most studies to date have looked at the evidence left behind after a collision simply to determine if the seat belt was being used. This study undertakes the next step and addresses the question of how the belt system was being used. Test data is also presented to allow investigators to determine if the retractor locked and remained locked during the collision or if it spooled out during the collision.

The results of 22 HYGE sled tests were analyzed to investigate the types and patterns of marks left behind. Frontal impact sled tests were conducted using a variety of dummy sizes and belt configurations including several types of belt misuse conditions. A standardized process of documenting seatbelt load marks using objective measurements was developed and used to catalog the marks left behind by the crash test dummies loading the seatbelt systems in frontal impacts. The results of this study give insight into some unusual seatbelt load mark patterns that have been observed in the field. The results also demonstrate how a careful analysis of the forensic seatbelt evidence combined with an understanding of occupant belt fit and accident geometry can determine not only if a seatbelt was being used during an accident, but how it was being used.