The Influence of Disabling Injuries on the Design of the Vehicle Front End for Pedestrian Safety

Pedestrians struck by motor vehicles constitute a global health problem accounting for nearly 270,000 deaths and 10 million injuries worldwide annually. This dissertation addresses one aspect of this global health problem from an engineering standpoint. Although pedestrian safety regulations exist, they have been criticized for only representing a narrow range of crash scenarios.
Most pedestrian crashes occur with the front of the vehicle impacting the pedestrian. The design of a vehicle front end and potential countermeasures to improve pedestrian safety is a challenging problem owing to both the complex nature of the design space as well as the risk of injury depending on the speed, stature, stance, impact location, geometry and stiffness of the front end. The complexity and breadth of the problem necessitates a comprehensive but efficient approach to the design of countermeasures. Multibody models have the potential to serve as excellent tools for such optimization studies owing to their computational efficiency, however, the biofidelity of these models is under question.
Traditionally, in the design of vehicles, the focus has been on minimizing the risk of fatalities. As countermeasures, regulations, and infrastructure are developed there is a trend towards fewer fatalities but injuries, albeit at potentially a lower severity, still exist. Many of these injuries have long-term consequences for the pedestrian survivors. The current pedestrian safety regulations rely on subsystem-based procedures. Experimental test devices have been developed that represent the head, thigh-pelvis, and lower extremities. Given the complexity of the pedestrian kinematics, the subsystem procedures alone are insufficient to evaluate the protection provided by the countermeasures. Additionally, there is a lack of a comprehensive cost model that can detect the effects of local design changes on the overall risk arising from a vehicle to pedestrian impact. Also, the influence of disabling injuries on the design of the vehicle front end remains unexplored.
This dissertation provides a framework for the assessment of disabling injuries on the design of the vehicle front end for pedestrian safety. Firstly, a multibody model of a pedestrian representing the 50th percentile male is developed and its biofidelity is assessed by a series of component level impact tests in conjunction with whole-body impacts with a generic pedestrian buck. Field data from pedestrian databases is analyzed to identify the representative pedestrian injuries based on frequency, and
their injury mechanisms are identified. With the aid of the Monte Carlo approach a cost function is developed to quantify the influence of both fatal and disabling injuries. The developed cost function in conjunction with the validated multibody pedestrian model is used to explore the primary objective of understanding the influence of disabling injuries on vehicle design (for pedestrian crashes). A design of experiment (DOE) is conducted by using a parameterized vehicle model representing a sedan impacting a 50th percentile male pedestrian at speeds of 40 km/hr and 25 km/hr.
The influence of disabling injuries on the vehicle design diminishes with increase in the speed of impact due to a higher risk of fatalities. In a hypothetical scenario where there are no head injuries (which are the leading cause of pedestrian fatalities) the cost associated with disability is more influential in affecting the vehicle design. Hence, it is important to consider the disability outcome while designing the countermeasures. While this dissertation focuses on pedestrian crash scenarios, the framework developed here can be applied during the design of a vehicle for other crash modes like frontal, rear, and oblique impacts.