Influence of Vehicle Front-End Design and Population Diversity in car-to-pedestrian collisions

Traumatic brain injuries (TBIs) remain one of the leading causes of death and long-term disability in road traffic accidents, with pedestrians representing a particularly vulnerable group. While occupant safety has improved significantly through airbags and seatbelts, pedestrians continue to face severe risks in car-to-pedestrian collisions (CPCs). Recent computational studies have highlighted that vehicle front-end design parameters and pedestrian body characteristics play a decisive role in determining head injury outcomes.

This research used realistic finite element (FE) vehicle models and detailed THUMS pedestrian models to reconstruct thirty-six CPC scenarios at speeds of 30, 40, and 50 km/h. The vehicles included a subcompact sedan (Toyota Yaris), a midsize sedan (Toyota Camry), and an SUV (Ford Explorer). Pedestrian models represented a diverse population: a 95th percentile male (AM95), a 50th percentile male (AM50), a 5th percentile female (AF05), and a six-year-old child (6YO). The study found that bonnet leading edge height (BLEH) was a critical predictor of pedestrian head injury risk. Smaller BLEH-to-center-of-gravity (CG) ratios correlated with reduced Head Injury Criterion (HIC) and Brain Injury Criterion (BrIC) values, particularly at higher speeds. For example, at 50 km/h, lower BLEH/CG ratios reduced lateral bending velocities and lowered HIC values with R² values up to 0.62. Conversely, vehicles with high BLEH and shallow bonnet angles were more likely to produce severe AIS 4+ head injuries, especially in taller pedestrians.

Population diversity also mattered. Children and shorter pedestrians were more likely to sustain head impacts near the bumper or grille, while taller pedestrians experienced bonnet or windshield contact. These differences translated into distinct injury mechanisms: linear head kinematics dominated focal injuries such as skull fractures, while rotational dynamics drove diffuse injuries like concussion and diffuse axonal injury (DAI). The computational approach also validated vehicle and pedestrian models against cadaveric data and Euro NCAP protocols, ensuring biomechanical accuracy. Improved windshield modeling, using a three-layer glass-PVC-glass structure, enhanced prediction of fracture patterns and headform accelerations, aligning closely with experimental results. Despite these advances, limitations remain. Correlations between BLEH/CG ratios and injury metrics were moderate (R² values between 0.2–0.5 in many cases), and simulations were restricted to mid-stance walking postures and centerline impacts. More complex gait postures and oblique collisions could alter injury outcomes. Additionally, detailed brain models were not available for child pedestrians, limiting intracranial strain analysis in those cases.

In conclusion, this study demonstrates that vehicle front-end geometry and pedestrian body size are key determinants of head injury risk in CPCs. By integrating these insights into vehicle design, automakers can better protect pedestrians, reducing the likelihood and severity of TBIs. Computational modeling thus provides a powerful foundation for proactive pedestrian safety strategies.

References

Otte, D. (1999). Injury mechanism and protection of pedestrians in accidents. Accident Analysis & Prevention.
Li, F., Shang, S., et al. (2017). Influence of vehicle front shape parameters on pedestrian head injuries. Accident Analysis & Prevention.
Watanabe, R., et al. (2011). Numerical study of pedestrian head injuries using THUMS models. Stapp Car Crash Journal.
Kerrigan, J., et al. (2005). Pedestrian injury biomechanics in SUV impacts. Stapp Car Crash Journal.
Kerrigan, J., et al. (2007). Pedestrian injury biomechanics in mid-size sedan impacts. Stapp Car Crash Journal. Peng, Y., et al. (2013). Windshield modeling and validation for pedestrian safety simulations. International Journal of Automotive Technology.
Public Health Agency of Canada (2020). Sentinel surveillance of pedestrian head injuries in RTAs.