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The use of booster cushions by children more than 3 years old is a relatively new behaviour in FRANCE. In fact, the restraint of children in systems adapted to their age and anthropometry, has only been mandatory since January 1st, 1992. The french car manufacturers have tested, during the last years, a great number of boosters in a car environment. In particular a comparative study between “simple” cushions and boosters with a back-rest -in order to satisfy parents requiring better comfort for their children- has been undertaken. On the basis of these tests, the manufacturers have made a selection for their cars, according to a certain number of criteria which will be described. It it well known that the main advantage of boosters is to be very easy of use. A complementary accidentological analysis made recently in FRANCE reveals however some problems of injuries linked to misuse of these restraint systems. Studies are in progress in order to assess consequences of these misuses.

In frontal impact, the occupantlbelt interaction is essential to obtain a good simulation of the occupant dynamic behaviour. Nevertheless, current mathematical models do not allow a realistic representation of this interaction to be obtained. Especially they are not adapted to simulate two important phenomena: the chest and pelvis deformation under the belt loading, and the belt sliding on the occupant. This paper deals with a tridimensional finite element model which allows an improved simulation of this interaction. The Hybrid III dummy, restrained by a 3-point retractor belt, was aimed, with a finite element program (RADIOSS). The model consisted of two parts: a deformable part representing, by means of springs and shell elements, the belt system, the thorax and the- pelvis; a rigid part representing, with rigid shell elements, the other components of the system. The belt was simulated by shell elements with a elasto-plastic material law.

No method based on experiments is convenient for evaluating globally the potential risk of a given vehicle for the whole population of pedestrians at risk, which encompasses the smallest children and the tallest adults simultaneously, when a large range of impact speeds has to be considered. Mathematical models are also inadequate, due to the large number of runs required for obtaining the probability of impact on each section of the front end profile. This paper describes first a recently improved mathematical method for defining the head trajectories yielded by experimental simulations or by a validated mathematical model. Then, a computer program is presented that simultaneously uses this method and statistical data concerning real accidents. The output of this program is a distribution of the impact probabilities for a given profile. The head impact velocities can be utilized for weighing the results. Possible improvements and application of this method are discussed.

Experimental car-pedestrian collisions were performed with a modified PART 572 dummy and cadavers; they involved some reconstructions of real accidents. These collisions brought to light the differences between the kinematics and the impact responses when dummy and human subject are compared under identical and realistic test conditions to simulate a pedestrian struck sideways. These differences are mainly due to the overall relative stiffness of the PART 572 dummy when compared to cadavers. Same-type collisions were therefore carried out again with other dummies which were designed so as to simulate human response in lateral impact better; thus they were also assumed to display better kinematics as pedestrians. APROD and ONSER dummies were used; when compared to PART 572, their flexibility and deformation capabilities are greater, in particular as regards their thoraxes and shoulders.

Protection criteria aside from deflection are defined on the basis of measurement functions taken at various but unique points on the thorax (rib, spinal column); these functions may also use two points (two ribs, for example) which results in deflection intervening as a criterion. The conditions imposed by these criteria result in different requirements for vehicle wall conditions and thorax model construction. Mathematical modeling of the vehicle wall-thorax collision is performed in order to compare possible criteria on this basis. Concurrently, a statistical analysis performed on a sampling of side impacts occurring with human subjects permits injury severity to be expressed by means of several functions whose predictive qualities are unequal. These functions include deflection, and their literal expression takes into account the state of the subjects' bone structure. The criteria produced by these predictive functions are used in the preceding mathematical model.

Safety of children as car occupants raises a specific problem: it is necessary to take into account two factors which are particular to them: their very fast growth and their behavior, which corresponds to a need for movement. An analysis of statistical and accidentological data, points to the fact that whereas traffic accidents account for 25 % of adult deaths, they account for nearly 50 % of deaths for children (all kinds of road-users). Measures were adopted in France; such as the obligation for children of less than 10-years-old to travel on rear seats of cars and the definition of an homologation procedure for children restraint devices, with the aim of limiting the consequences of these accidents. The most common restraint devices look like little individual seats and are designed to protect young children (less than 3-years-old). Recently, new restraint devices, called “cushions”, were developed.

Biomechanical studies related to the head have been mainly directed towards the determination of cerebral tolerance to impact in the absence of fracture. However, the frequency of skull trauma producing complex fractures and cerebral lesions linked to these fractures should be taken into consideration. On a human being, impacts under similar mechanical conditons can produce either fatal encephalic lesions without fractures or skull fractures with encephalic lesions if the subject has a different skull morphology. A sample of 146 subjects has been studied to determine the relation between the morphological characteristics of the skulls (weight of the skull cap, thickness, weight of the cranial skeleton…), their mineralization. The mechanical tests were performed on bone fragments (bending and shearing tests). Nine accelerometers were used during the experiments of various types of impacts. The results were computerized. The skull fractures observed (a total of 45) are described.

Experimental simulations of car pedestrian collisions were conducted with production cars impacting a pedestrian dummy derived from PART 572 ; the tests were performed under well standardized conditions to try to limit experimental dispersions. The results corresponding to one series of tests are presented. The comparison of kinematical behaviour of this dummy and human subjects impacted by an other way under identical realistic test conditions displayed differences in kinematics and response at impact between these two kinds of surrogates. These differences can be explained largely by the greater stiffness of the PART 572 dummy, as compared to human subjects. For this reason, it was determined to duplicate the tests performed with the PART 572 dummy with a new series of tests with one APROD dummy, modified in a pedestrian version.

This paper is related to the pedestrians struck by a vehicle. From the results of multiple runs performed with a previously validated mathematical model, an equation is defined which describes the trajectories of their heads. When the distribution in heights of the pedestrians and the distribution in speeds of the colliding vehicles are taken into account, this equation enables the prediction of the head impact probability for the sundry areas of the front end of the vehicle, according to its profile.

Car-pedestrian accidents were selected with reference to criteria like relevance in terms of injury severities representativity and reproducibility aiming to as accurate as possible reconstructions by dummy and cadaver tests. Parameters necessary for performance of these reconstructions were evaluated from the data of accident investigation teams. Preliminary tests were performed by research departments of automobile manufacturers to check the estimated conditions of these accidents before performing their reconstructions. A particular aim was to obtain insights into the mechanisms leading to injuries in pedestrian accidents; more generally reconstructing actual accidents is a privilegied approach to determine human tolerance limits and the corresponding protection criteria on dummies; the injuries resulting from the actual accidents are consequently compared with the data measured on dummies and cadavers in the reconstruction experiments.

A large number of experiments involving cadavers - including real-world-accident reconstructions - have been performed for the purpose of enhancing the state of knowledge concerning tolerance levels and protection criteria relevant to side-impact conditions. However, the scatter of the findings, as well as the considerable differences in injury severity levels (differences that cannot be accounted for by age differences alone) have limited the conclusions that it was possible to draw from these investigations in terms of criteria, mainly concerning thoracic protection. The major cause of scatter is the considerable differences in skeleton quality between subjects. Analysis of the rib characterization test findings made it possible to define a thoracic resistance index enabling the establishment of a classification of subjects. This index, which was validated with our sample, allowed us to evaluate the pertinence of the various side-impact protection criteria considered.