Publication

Deaths caused by road traffic crashes worldwide increased from 1.15 to 1.35 million from 2000 to 2016 [1].
Passenger car occupants account for the majority of these deaths [2]. In frontal impacts, the thorax is the most frequently injured body region for occupants sitting in the front [3], and the majority of these injuries are rib and sternum fractures [4].  
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 [5].  
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 [7]. 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 [8].  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  [7][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 [7].
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  [8].  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 [8].
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.