Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article


Master of Engineering Science


Mechanical and Materials Engineering


Mao Haojie


With the increasing prevalence of traumatic brain injuries (TBIs) in road traffic accidents (RTAs), it was identified that the shape of the vehicle's front end and pedestrian postures prior to impact significantly influence pedestrian head injuries. However, the effect of vehicle front shape parameters and gait postures on TBIs sustained in car-to-pedestrian collisions (CPCs) has yet to be quantified. This study used a computational approach to analyze the effect of vehicle shape parameters and pedestrian gait postures on pedestrian TBI risks across a diverse pedestrian population with varying body sizes. Our findings indicate that vehicle shape parameter such as BLEH (Bonnet leading edge height), BA (Bonnet angle), and WA (Windshield angle) were statistically significant predictors of pedestrians' TBI risk. Increasing BLEH in sedans and decreasing BLEH in high-leading-edged vehicles reduce the risk of TBIs. Vehicles with high BLEH and low BA were susceptible to AIS (Abbreviated injury scale) 4+ head injuries. In vehicles with a low BLEH, pedestrian height and mass were statistically significant factors affecting pedestrian head rotation. Our results demonstrate that TBI risks were found to be different for gait percentage in the same and different gait types. Walking and emergency gaits dominate linear head kinematics, whereas running gaits dominate head rotation in pedestrians, resulting in substantial brain strain. Linear head kinematics varies significantly between the stance and swing phases of walking and running gait postures, whereas rotational head kinematics and brain strains vary cyclically but to a less extent.

Summary for Lay Audience

In recent years technological advancements in seat belts and airbags have increased the survivability of vehicle occupants in road traffic accidents (RTAs). In contrast, pedestrians are still vulnerable to severe and fatal injuries in RTAs. Head injuries are leading causes of death and long-term disability. With different types of passenger cars and light trucks on the road, it was determined that the front shape of the car and pedestrian posture prior to the impact significantly influence pedestrian head injury risk. Numerous automakers attempted to optimize the vehicle front shape with soft and less stiff structures. As a result, several head injuries such as skull fracture and focal brain injuries were reduced, but the risk of diffuse brain injuries have become more common and has never been studied due to methodological constraints.

We adopted two novel computational approaches to investigate the impact of vehicle front shapes and pedestrian gait posture on pedestrian TBI risk using a full-scale FE pedestrian model. Our findings show that vehicle bonnet leading edge height (BLEH) has a significant impact on mild TBIs and that vehicles with higher BLEH, such as sports utility vehicles (SUVs) and pickup trucks, are more likely to cause severe head injuries. In addition, BLEH indirectly affects the pedestrian head rotation among different populations. Our findings also revealed that the risk of TBI varies depending on pedestrian pre-impact gait postures. These findings provide a basis for future vehicle design safety for pedestrian injury protection