Effects of vehicle front-end safety countermeasures on pedestrian head injury risk during ground impact

Pedestrian safety countermeasures such as pop-up bonnets and exterior pedestrian airbags have been shown to decrease the pedestrian injury risk caused by vehicle impacts (primary impact). However, it is still unknown whether these devices could prevent or mitigate pedestrian injuries resulting from ground impacts (secondary impact). In order to understand how the vehicle safety countermeasures prevent pedestrian head injuries caused by primary and secondary impacts, a total of 252 vehicle-to-pedestrian impact simulations were conducted using the MADYMO code. The simulations accounted for three types of vehicle configurations (a baseline vehicle and vehicles with the two aforementioned vehicle safety countermeasures) along with five front-end structural parameters at three vehicle impact velocities (30, 40, and 50 km/h). The simulation results show that the bonnet leading edge height was the most sensitive parameter affecting the head-to-vehicle impact location and that caused different head injuries resulting from the local stiffness in the location impacted. Moreover, the bonnet leading edge height was the leading governing factor on the pedestrian rotation angle in the secondary impact. The vehicle equipped with a pop-up bonnet and an external airbag could cause a larger pedestrian rotation angle at 30 km/h than that in the other two vehicle types, but conversely could cause a smaller pedestrian rotation angle at 40 and 50 km/h. Also, the vehicle equipped with pop-up bonnet and external airbag systems could lead a higher pedestrian flight altitude than that of the baseline type. A vehicle equipped with a pop-up bonnet and external airbag systems provide improved protection for the pedestrian’s head in the primary impact, but may not prevent the injury risk and/or even cause more severe injuries in secondary impacts.