The Effect of Pre-Crash Braking on Thoracic Injuries in Frontal Impacts
Deaths caused by road traffic crashes worldwide increased from 1.15 to 1.35 million from 2000 to 2016 .
Passenger car occupants account for the majority of these deaths . In frontal impacts, the thorax is the most frequently injured body region for occupants sitting in the front , and the majority of these injuries are rib and sternum fractures .
Field data show that thoracic injury risk, as with other injury risks, increases with delta-V and occupant age [4– 5]. Furthermore, thoracic injury risk has been shown to increase significantly for females and for those with a high Body Mass Index (BMI), while the effects of occupant height and vehicle model were not significant .
Automated Emergency Braking (AEB) helps to avoid collisions or to mitigate their consequences by lowering
the impact speed, which leads to a lower thoracic injury risk [6-7]. However, few studies have addressed the effects of AEB on injury risk at identical impact speeds. Car occupants move forward during braking, due to inertia, and therefore have a forward displaced position at the beginning of the crash phase compared to a situation without braking . Analysis of the Institute for Traffic Accident Research and Data Analysis (ITARDA) field data has shown that pre-crash braking increases thoracic injury risk at equal impact speeds as cited in . The effect of AEB on injury risk at identical impact speeds merits further investigation to identify the injury mechanisms and prevent the injuries with the development of appropriate technology.
Previous finite element (FE) simulation studies with human body models (HBMs) addressing this question obtained contradictory results. Studies using the Total HUman Model for Safety (THUMS), PIPER paediatric HBMs and the Hybrid III dummy have reported lower thoracic injury risk with AEB than without, at identical impact speeds [9–10]. This was mainly due to an increase in the ride-down effect as a result of earlier coupling between the airbag and the occupant .
However, a study using the Japan Automobile Manufacturers Association (JAMA) human FE model found that with AEB the injury risk was higher because of the changes in occupant posture, which led to greater rotation of the torso . The earlier interaction of the airbag with the upper body was also reported to contribute to the higher injury risk because of a so-called membrane loading phenomenon, i.e., the wrapping of the airbag around the upper thorax and neck of the occupant produces a strong force over a large area, when the occupant is out- of-position and too close to the airbag .
This study aimed to assess the effects of pre-crash braking on thoracic injuries, particularly rib fractures, sustained by occupants in frontal car crashes by means of both FE simulation with HBMs and field data analysis.