Vehicle frontal protection system geometry and pedestrian impacts: the effect of AS 4876.1-2002 geometric criteria

Abstract

Australian Standard AS 4876.1-2002 stipulates requirements for motor vehicle frontal protection systems (VFPS), colloquially known as bull bars. Section 2 of the Standard sets design and installation requirements and has a particular focus on the geometry of the VFPS, stipulating that their geometry should generally conform to the frontal shape of the vehicle. The aim of this project was to examine the differences between pedestrian impacts with vehicles fitted with a VFPS with geometry that meets the requirements of Section 2 of AS48761.1-2002 and VFPS that do not meet these requirements. MADYMO was used to simulate pedestrian impacts with vehicles that had VFPS fitted. The simulations showed that conforming VFPS tend to redistribute impact forces to contacts with the bumper section of the VFPS. For an SUV impact, the increase in risk of pelvic injury produced by this change in loading pattern is only marginally offset by a small reduction in the probability of upper leg injury. For a sedan impact, increased risk in upper leg injury may be offset by a reduction in risk to lower leg injury, depending on the material of the VFPS. Conforming VFPS also tended to result in lower head impact speeds with the vehicle, reducing the severity of the impact with the head, resulting in a reduction in risk of serious head injury well over 50% based on the change in the head injury criterion. The extent to which the results of the narrow set of impact conditions studied can be generalised to all collisions is not completely clear, although it seems reasonable to suggest that the effects will apply where the interaction with the bull bar and the pedestrian is at, or below, the pelvic region. It is less likely that the geometry of the bull bar would affect children to the same extent. The results of this brief simulation study support the expectation that the adoption of Section 2 of AS 4876.1-2002 will lead to reductions in injury risk to people struck by VFPS.