# Evaluation of Urban Traffic Accidents Based on Pedestrian Landing Injury Risks
## 1 Introduction  
The World Health Organization (WHO) has released the Global Status Report on Road Safety, which shows that approximately 1.35 million people die annually from road traffic accidents. More than half of all deaths are among those with the least protection: pedestrians (23%), cyclists (3%), and motorcyclists (28%) [1]. Recent trends in traffic safety research show that scientists and industry are making tremendous efforts to find solutions to improve the safety and performance of vehicle systems [2; 3; 4]. For decades, scholars have focused on road safety research in vehicle-to-pedestrian collisions, and a variety of vehicle safety protection devices and vehicle optimization designs have been proposed [5; 6; 7; 8; 9; 10; 11; 12; 13]. However, it should be noted that the injuries suffered by pedestrians in road traffic do not only come from vehicles, but also from the ground. The real-world accident data analysis has shown that ground contact plays a very important role in the cause of pedestrian head injuries [14; 15; 16]. While there are still few studies on pedestrian-to-ground contact [17; 18; 19; 20; 21; 22; 23; 24; 25; 26; 27]. The main reason is that it is difficult foraccident investigators to obtain the impact traces between pedestrians and the ground, compared to pedestrian-to-vehicle contact. In addition, the injury risk from ground was correlated to a lesser extent with vehicle velocity [17; 21], and the ground usually results in more unpredictable injuries [28]. In recent years, some researchers have studied the kinematics of pedestrian landing and have come up with several typical types of pedestrian landing kinematics [17; 19; 25; 29], this provided an understanding for pedestrian-to-ground contact; however, they did not deeply analyze the influence mechanism of landing kinematics on landing injuries. In 2018, [PERSON] et al. [21] proposed the concept of the pedestrian rotation angle ranges (PRARs) to illustrate the relationship between pedestrian landing kinematics and landing injuries, which demonstrated that any landing kinematics could be classified as one of the four PRARs, and the PRARs are highly correlated with the ground contact mechanism and head injury risk. However, pedestrian landing kinematics and injury risk are not only affected by pedestrian rotation angle, but also by a variety of other factors, such as the pedestrian facing orientations and the landing sequence of body parts, which they did not analyze. Further study found that for the same pedestrian rotation angle, there were significant differences in the risk of head injury during landing for different pedestrian facing orientations [30]. However, they did not delve into the mechanism between this factor and pedestrian injury risk. Having a look at the literature review, it was found that the biomechanical mechanisms of pedestrian injury is closely related to the symmetric/asymmetric phenomena (structures, shapes, morphologies, geometry, direction, models, aesthetics, etc.) in life sciences [31; 32]. In response to this intriguing problem, this paper systematically and quantitatively investigated the effect of human anatomy features on body landing injury risk by considering two key kinematic parameters, pedestrian rotation angle (PRA) and pedestrian facing orientation (PFO). To this end, six real-world pedestrian accidents were reconstructed to derive the boundary parameters at the moment of body-to-ground impact. Then, a total of 24 pedestrian landing simulations were carried out using the THUMS v4.0.2 model with considering eight PRAs and three PFOs. The kinematic-based injury criteria such as the head injury criterion (HIC) and the maximum rotation angle of T1 relative to the head were included in the analysis to investigate head and neck injury risk. Moreover, the influence mechanism of human anatomical symmetry/asymmetry on the risk of landing injuries was deeply analyzed.