Pedestrian headform testing: inferring performance at impact speeds and for headform masses not tested, and estimating average performance in a range of real-world conditions.

OBJECTIVE: Tests are routinely conducted where instrumented headforms are projected at the fronts of cars to assess pedestrian safety. Better information would be obtained by accounting for performance over the range of expected impact conditions in the field. Moreover, methods will be required to integrate the assessment of secondary safety performance with primary safety systems that reduce the speeds of impacts. Thus, we discuss how to estimate performance over a range of impact conditions from performance in one test and how this information can be combined with information on the probability of different impact speeds to provide a balanced assessment of pedestrian safety. METHOD: Theoretical consideration is given to 2 distinct aspects to impact safety performance: the test impact severity (measured by the head injury criterion, HIC) at a speed at which a structure does not bottom out and the speed at which bottoming out occurs. Further considerations are given to an injury risk function, the distribution of impact speeds likely in the field, and the effect of primary safety systems on impact speeds. These are used to calculate curves that estimate injuriousness for combinations of test HIC, bottoming out speed, and alternative distributions of impact speeds. RESULTS: The injuriousness of a structure that may be struck by the head of a pedestrian depends not only on the result of the impact test but also the bottoming out speed and the distribution of impact speeds. Example calculations indicate that the relationship between the test HIC and injuriousness extends over a larger range than is presently used by the European New Car Assessment Programme (Euro NCAP), that bottoming out at speeds only slightly higher than the test speed can significantly increase the injuriousness of an impact location and that effective primary safety systems that reduce impact speeds significantly modify the relationship between the test HIC and injuriousness. CONCLUSIONS: Present testing regimes do not take fully into account the relationship between impact severity and variations in impact conditions. Instead, they assess injury risk at a single impact speed. Hence, they may fail to differentiate risks due to the effects of bottoming out under different impact conditions. Because the level of injuriousness changes across a wide range of HIC values, even slight improvements to very stiff structures need to be encouraged through testing. Indications are that the potential of autonomous braking systems is substantial and needs to be weighted highly in vehicle safety assessments.

From crash test speed to performance in real world conditions: a conceptual model and its application to underhood clearance in pedestrian head tests.

Current safety testing protocols typically evaluate performance at a single test speed, which may have undesirable side effects if vehicles are optimised to perform at that speed without consideration to performance at other speeds. One way of overcoming this problem is by using an evaluation that incorporates the distribution of speeds that would be encountered in real crashes, the relationship between test speed and test performance, and the relationship between test performance and injury risk. Such an evaluation is presented in this paper and is applied to pedestrian headform testing. The applicable distribution of pedestrian impact speeds was compiled from in-depth crash data. Values of the Head Injury Criterion across the speed distribution were imputed from a single test result, taking into account the potential for 'bottoming out' on harder structures beneath the hood. Two different risk functions were used: skull fracture risk and fatal head injury risk. Eight example test locations were evaluated; each had an underhood clearance such that it would perform worse at higher speeds than suggested by its original test result. When the effect of bottoming out was included in the evaluation, the calculated average injury risk was generally higher than it was if bottoming out was ignored. The average risk of fatal head injury was more affected by the inclusion of bottoming out than the average skull fracture risk. The methodology presented in this paper may be extended to other forms of impact testing, although the input functions may be more difficult to derive for more complex tests.

Using child age or weight in selecting type of in-vehicle restraint: implications for promotion and design.

A survey of motor vehicle child restraint use found around 28% of children under the age of six using weight-inappropriate restraints. Many parents did not know when a child was likely to outgrow a booster seat nor the weight of their child, but they did know the child's age. Anthropometric data show that, if advice on restraint transition, given solely in terms of age (6 months, 4 years, 8 years) were followed in Australia, incorrect restraint selection would occur in 5% of children under the age of six. Further analysis suggests how rewriting the Standard could reduce this number. We present an argument for placing age-based transitions at the heart of the strategy to improve child restraint compliance. This may be superior to one based on the child's weight or other anthropometric measurement. Our argument may be summarized as follows: 1 Age-based rules for selecting child restraints are simple, require less information to be retained, and might be more natural criteria for parents. They might have a greater chance of being adopted as norms, and of encouraging good peer cues. Anthropometric rules, on the other hand, assume that parents know the current dimensions of their children and have the tools at their disposal to measure these dimensions. 2 The consequences of age-based promotion for the proportion of children in a restraint suitable for their weight can be estimated for alternative regulatory frameworks. We will report such Calculations below and show that this rate can potentially be very high. The rate would be even higher if child restraint design standards were drafted with age-based transitions in mind. Age-based transitions imply restraint specifications (weight and height limits) that can be determined from anthropometric survey data. 3 Such standards would necessarily imply overlapping anthropometric ranges for the different types of restraint. However, we emphasize that these overlaps would exist to facilitate age-based transitions, not to feature in publicity advising on the correct selection of child restraints. Under such a regime, promotion is driven by what information is readily usable by parents, and ceases being consequential to the standards-setting process. In support of this argument we shall report a survey of restraint use among parents of pre-school and school aged children, and an analysis of the weights (or other dimensions) of children that provides a technique for estimating how well age-based transition could work. The remainder of this paper is divided into sections covering the survey and the anthropometric study. These are synthesized in a discussion of their implications for restraint promotions and standards setting.

Modelling errors in scoring the darkness of staining.

OBJECTIVE: To construct a statistical model for the agreements and disagreements between two observers on darkness of staining. STUDY DESIGN: Data from an earlier observer-agreement study by van Diest et al were reanalyzed. RESULTS: A model in which the random variation in error is permitted to depend upon the true darkness of staining wasfound tofit the data much better than does one in which the random variation is constant. CONCLUSION: For the dataset analyzed, error tends to be greater (that is, correlation between observers tends to be less) when staining is darker.