Pedestrian Subsystem Research Articles

Have pedestrian subsystem tests improved passenger car front shape?

Subsystem impactor tests are the main approaches for evaluation of safety performance of vehicle front design for pedestrian protection in legislative regulations. However, the main aspects of vehicle safety for pedestrians are shape and stiffness, and though it is clear that subsystem impact tests encourage lower vehicle front stiffness, it is unclear whether they promote improved vehicle front shapes for pedestrian protection. The purpose of this paper is therefore to investigate the effects of European pedestrian safety regulations on passenger car front shape and pedestrian injury risk using recent German In-Depth Accident Study (GIDAS) pedestrian collision data and numerical simulations. Firstly, a sample of 579 pedestrian collision cases involving 190 different car models between 2000–2015 extracted from the GIDAS was used to compare front-end shapes of passenger cars manufactured before and after the legislative pedestrian safety regulations were introduced in Europe. The focus was on changes in passenger car front shape and differences in pedestrian AIS2+ (Abbreviated Injury Scale at least level 2) leg, pelvis/femur and head injury risk observed in collisions. Multi-body simulations were also used to assess changes in vehicle aggressivity due to the observed changes in vehicle shape. The results show that newer passenger cars tend to have a flatter and wider bumper, higher bonnet leading edge, shorter and steeper bonnet and a shallower windscreen. Both the collision data and the numerical simulations indicate that newer passenger car front bumper designs are significantly safer for pedestrians’ legs. However, the results also show that the higher bonnet leading edge in newer passenger cars is poor for pedestrian pelvis/femur protection, even though newer cars show an obviously lower AIS2+ injury risk to younger pedestrians in collisions. Newer cars have a lower AIS2+ head injury risk for pedestrians in collisions, but the numerical analysis indicate that this is not likely due to shape changes in passenger car fronts. Overall, the introduction of pedestrian safety regulations has resulted in reductions in pedestrian injury risk, but further benefits would accrue from tests which promote a lower bonnet leading edge. The influence of vehicle shape on pedestrian head injury risk remains unclear.

An Analysis of Head Impact Severity in Simulations of Collisions Between Pedestrians and SUVs/Work Utility Vehicles, and Sedans

Objective: To describe the determinants of the severity of the head kinematics of a pedestrian when struck by common sport utility vehicles (SUV) and work utility vehicles (WUVs) to assess how effective assessment protocols are in assessing injury risk for SUVs and work utilities. Methods: Three hundred twenty-four simulations of pedestrian collisions with SUVs, work utility vehicles, and sedans were performed using several vehicle geometries, pedestrian orientations, speeds, and braking levels. Contact stiffnesses in the models were based on impact test results with exemplar vehicle structures. A single contact characteristic was used for all head-to-hood contacts to allow the effects of other factors on head injury risk to be compared. Simulations of standard headform tests on the same hood characterized the structure from a subsystem test perspective. Results: Head injury criterion values were higher in SUV/WUV simulations than sedan simulations because of high neck tension rather than through higher contact forces with the hood. In fact, the severity of the impact between the head and hood was slightly less in SUV/WUV simulations. Sedan and SUV/WUV simulations produced lower head injury criterion (HIC) values than did the subsystem tests. Conclusions: High bonnet leading edges led to increased neck loads in these simulations of pedestrian collisions. Neck loads were influential on head injury risk in the SUV/work utility simulations but not in sedan simulations. Subsystem impact tests may overestimate head impact risk from the hood itself but fail to capture a potentially important injury mechanism in collisions with vehicles with high leading edges and thus fail to differentiate completely risks posed by such vehicles. These results may have implications for the interpretation of pedestrian subsystem test results: a given HIC value in an SUV/WUV test may represent a relatively higher risk of injury than the same results recorded in a sedan test.

Effects of vehicle bumper height and impact velocity on type of lower extremity injury in vehicle–pedestrian accidents

In nonfatal passenger vehicle–pedestrian accidents, the lower extremities are the most commonly injured body parts. The European Enhanced Vehicle-safety Committee Working Group 17 (EEVC/WG17) pedestrian subsystem test method using a legform impactor has been developed mainly for evaluation of aggressiveness of the front bumper of passenger vehicles. However, in recent years the number of sports utility vehicles (SUV) with a high bumper has been rapidly increasing. Since the bumper height is different between a passenger vehicle and an SUV, the type of lower extremity injury may be different. The type of lower extremity injury caused by this different bumper height should be clarified, because the test method and vehicle safety countermeasure must take into account a certain type of injury. Furthermore, the effect of vehicle impact velocity on the type of lower extremity injury in vehicle–pedestrian accidents has not been investigated so far. Therefore, the objective of this study is to clarify the effect of vehicle bumper height and vehicle impact velocity on the type of lower extremity injury in vehicle–pedestrian accidents. The Pedestrian Crash Data Study (PCDS), an in-depth accident database in the USA, was used for the current analyses. The results indicate that the type of injury, i.e., to the tibia and knee ligament, could become an injury to the femur with an increase in bumper height. Furthermore, the main injury at an impact velocity of around 20–30 km/h is to the knee ligament. On the other hand, the main injury at an impact velocity of around 40 km/h is a fracture of the lower extremities.

Evaluation of Pedestrian Subsystem Test Method Using Legform and Upper Legform Impactors for Assessment of High-Bumper Vehicle Aggressiveness

In accidents involving sports utility vehicles (SUVs), injuries to pedestrian leg, knee ligaments, and femur are likely to occur. Therefore, the European Enhanced Vehicle Safety Committee proposed two subsystem test methods for evaluation of SUV bumper aggressiveness. Such evaluation can be conducted by means of either a legform impactor (evaluation of risk of knee and tibia injury), or an upper legform impactor (evaluation of risk of thigh and pelvis injury) test. Each of these two test methods has its own injury criteria and injury acceptance levels. Therefore, the first objective of this research is to clarify any differences between the test results obtained when evaluating SUV bumper aggressiveness by means of these two impactors. The second objective is to determine whether or not a legform impactor can be applied to estimate the risk of femur fracture, and if an upper legform impactor can be used to estimate the risk of knee ligament injury. The present results indicate the test method using an upper legform impactor yields higher ratios of injury criteria to the relevant EEVC/WG17 injury acceptance levels than by using a legform impactor. Thus, the upper legform impactor test rates an SUV bumper as more aggressive than the legform impactor test. The present study suggests the lower leg acceleration obtained by the legform impactor can be used to adequately assess the risk of femur fracture, when evaluating the aggressiveness of an SUV bumper using proposed injury acceptance levels reported in the literature. Similarly, the impact force obtained by the upper legform impactor can be used to assess the risk of cruciate ligament injury.

Pedestrian subsystem head impact results reflect the severity of pedestrian head injuries

Ten head impacts between pedestrians and cars were reconstructed to compare the head injuries sustained by pedestrians with the results of reconstruction tests using the headform impactors designated by the European Enhanced Vehicle-safety Committee (EEVC) Working Group 10 for assessing pedestrian head protection. The methodology of this study included at-scene accident investigation, computer simulation, and physical reconstruction in a laboratory of the head impacts that occurred in the accident cases that were investigated. The main finding was that the results from using the EEVC headform impactors test correlate well with the severity of any head injury, as measured by the Abbreviated Injury Scale, in actual pedestrian accidents. Head impacts that exceeded a HIC value of 1000 were positively associated with head injuries that were AIS3 or above.

Development of computer simulation models for pedestrian subsystem impact tests

The European Enhanced Vehicle-safety Committee (EEVC/WG10 and WG17) proposed three component subsystem tests for cars to assess pedestrian protection. The objective of this study is to develop computer simulation models of the EEVC pedestrian subsystem tests. These models are available to develop a car conforming to the pedestrian subsystem test requirements. The pedestrian subsystem test models were developed and validated in this study. However, some improvements are still needed in these models to make them more reliable in simulating the pedestrian subsystem tests to develop a car conforming to the test requirements.