Dangers of Seatback Recline in a Moving Vehicle: How Seatback Recline Increases the Injury Severity and Shifts Injury Pattern
Authors: Thorbole Chandrashekhar K. 
Published: March 2016

The seatbelt is the most important safety device that saves the life during vehicle collisions. The majority of vehicles available today are equipped with the conventional single loop three-point belt systems. In this belt system for the front outboard positions, the shoulder anchor point (D-Ring) is fixed on the vehicle B-pillar. Vehicle manufacturers are required to show the compliance with established FMVSS regulations ensuring adequate safety performance of restraint system during a frontal crash scenario. This performance evaluation is based on the study of the biomechanical response of the crash dummy used. In these evaluations, the front outboard seats and respective seatbacks are set to be based on manufacturers nominal riding position that usually consist of seatback recline less than 20 deg with vertical. The conventional belt and its fit around the occupant are the function of seatback recline angle. The belt fit get worse with higher seatback recline angles and reduce the level of protection offered during a frontal crash scenario. In some situations, this condition also causes severe to critical injuries.

The purpose of this study was to conduct research on the effect of automotive reclined seatback in a moving vehicle on the deterioration of occupant protection and modification in the injury pattern. A real world case is investigated and presented in this paper explaining the dangers of reclined seat in moving a car with a conventional belt system. The investigation involved a detailed study of crash reports, Medical documents, medical scans, accident reconstruction, vehicle inspection, witness statements and other pertinent crash related facts. A surrogate study is conducted on a similar vehicle to identify occupant’s body configuration with respect to various interior components of the vehicle including the seatbelt webbing. The surrogate study also facilitates the understanding of interior marks generated by occupant contact during secondary impacts. A detailed injury mechanism analysis is conducted to identify the best injury prevention countermeasure in such scenario. The injured occupant sustained cervical spinal cord injury in this crash. Abdomen fat stranding analysis is conducted to conclude the lap belt submarining in the crash with reclined seatback.

An MADYMO computer modeling study is conducted to explain the occupant kinematics in this frontal crash with reclined seatback and locked hanging shoulder portion of the webbing. The analysis provides insight regarding the kinematics and body interaction with various involved physical components inside the vehicle. This model shows submarining of the pelvis under lap belt that shows occupants vulnerability for abdomen injuries along with other associated severe injuries. The altered kinematics causes occupants neck to interact with the locked shoulder portion of the seatbelt. This knowledge is extremely important for the development of the best injury prevention schemes by improving the crashworthy performance of the vehicle to prevent such injuries.