Pedestrian Collisions with Flat-Fronted Vehicles: Injury Patterns and Importance of Rotational Accelerations as a Predictor for Traumatic Brain Injury (TBI)

Research on pedestrian protection currently is focusing mainly on passenger cars. However, impacts with heavy goods vehicles (HGV) and buses are also important, especially in urban areas and in developing countries. This study is an attempt to show the distribution of injury patterns focused on the head injury mechanism. In the European project APOLLO WPII database with a number of 104 pedestrians injured by a HGV or bus were identified. The head was found the most severely injured anatomic region, with an average AIS of 3.1, followed by the abdomen/pelvis (AIS 2.9), and the thorax (AIS 2.1). Using the Dr. Martin transformation matrix, head injury mechanisms were assigned to codified head injuries. Around 69% of the sustained head injuries had a rotational injury mechanism, 21% translational, and 10% either. Three multi-body vehicle models, representing two HGV and one bus, were used in a large parameter analysis. The simulations showed that the angular velocity change is exceeding 30rad/s and the angular acceleration is exceeding 10.000rad/s² in simulations where the HIC value was below 1000. Additionally the head injury risk was assessed by prescribing the accelerations of the human pedestrian model’s head to a finite element head and brain model. It can be concluded that head injuries are the most frequent injuries sustained by pedestrians involved in a collision with a flat-fronted vehicle and rotational accelerations are responsible for around 70% of head injuries. Impactors currently used in pedestrian protection regulations do not assess rotation-induced injuries.