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 “a VFPS shall have a profile that generally conforms to the shape, in plain view, front view and side view, of the front of the vehicle to which it is fitted” (Standards Australia, 2002). South Australia has recently adopted Section 2 of the Standard, specifying that new vehicles sold after the 1st of July 2013 may only be fitted with a VFPS that conforms to the requirements of Section 2. 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. In the simulations, the VFPS were attached rigidly to either a Sports Utility Vehicle or a sedan vehicle model. The SUV vehicle model was based on a 2006 Nissan Patrol. The sedan vehicle model had geometry based on a Holden (General Motors) Commodore from 2006. To represent nonconforming VFPS in the simulations the position of the top bar on each of the VFPS was moved forward. Two such configurations were produced. The first nonconforming configuration was termed ‘in line’ because the top bar was positioned in line with the bar directly below it. The second nonconforming configuration was termed ‘forward’ as the top bar was positioned forward of the bar directly below it. The vehicle was set to have an initial speed of 40 km/h at impact between the standard VFPS configuration and the pedestrian. An acceleration of -0.75g was applied to the vehicle over the complete duration of the simulation to represent emergency braking. VFPS geometry affects injury risk in these simulations through two main mechanisms. In the first case, 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. In the second case, conforming bull bars tended to result in lower head impact speeds with the vehicle, reducing the severity of the impact with the head. In our simulations of SUV pedestrian impacts, the reduction in risk of serious head injury was well over 50% based on the change in the head injury criterion, commensurate with what might be expected based on the change in the head impact speed. The relatively benign effects of conformity for sedan impacts should be viewed in light of research conducted by Doecke et al. (2008) that found that the vast majority of pedestrian exposure to VFPS came from SUVs, with only 12% attributed to sedans. VFPS regulation designed to protect pedestrians should therefore be weighted towards the SUV case. 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. (Author/publisher)
Samenvatting