Thierry Serre

Real accidents involving vulnerable road users: in-depth investigation, numerical simulation and experimental reconstitution with PMHS

Abstract This paper presents the methodology used to improve knowledge about vulnerable road users’ accidents and more specifically pedestrians or cyclists. This work is based on a complete analysis of real accidents from three different approaches: in-depth accident investigation, numerical simulation with multibody model and experimental reconstitution with PMHS subject. Accidents chosen from an in-depth multidisciplinary investigation are numerically modelled using a multibody software. Then, a parametric study focused for instance on car velocity and victim position at impact is performed in order to find the best correlations with all indications produced by the in-depth analysis. Finally, the retained configuration close to the presumed real accident conditions is reproduced experimentally by a crash test using cadavers. All results are finally compared in order to validate the real accident reconstruction. This methodology is applied on two real accidents involving one pedestrian or one cyclist.

Child pedestrian anthropometry: evaluation of potential impact points during a crash

This paper highlights the potential impact points of a child pedestrian during a crash with the front end of a vehicle. Child anthropometry was defined for ages between 3 and 15 years. It was based on the measurement of seven different segment body heights (knee, femur, pelvis, shoulder, neck, chin, vertex) performed on about 2,000 French children. For each dimension, the 5(th), 50(th) and 95(th) percentile values were reported, and the corresponding linear regression lines were given. Then these heights were confronted with three different vehicle shapes, corresponding to a passenger car, a sport utility vehicle and a light truck, to identify impact points. In particular, we show that the thigh is directly hit by the bumper for children above 12 years of age, whereas the head principally impacts the hood. The influence of child anthropometry on the pedestrian trajectory and the comparison with test procedures in regulation are discussed.

Comparison of the biomechanical behavior of the liver during frontal and lateral deceleration

BACKGROUND The trunk of a car occupant can be injured by a frontal or lateral impact. Lesions can be either intrusion injuries or due to the effects of deceleration alone. The aim of this study conducted with human cadavers was to explore the effects of deceleration on the liver during frontal or lateral deceleration. METHODS Trunks previously instrumented with accelerometers in three sites, the left and right lobes of the liver and the retrohepatic inferior vena cava, were subjected to substantial deceleration in three orientations: frontal, left, and right lateral. The anatomic consequences and deceleration data were measured. A deceleration ratio was defined as a peak deceleration measured in the liver divided by peak deceleration imposed on the trunk. RESULTS Peak deceleration imposed on the trunks was up to 60 g, which caused peak deceleration up to 26 g in the liver. No anatomic injury was observed. For each orientation, deceleration ratios were not significantly different among the three sites (p = 0.64) or between left and right lateral decelerations (p = 0.12). Deceleration ratios were significantly different (p = 0.001) between frontal (3 sites combined) and lateral (3 sites of left and right lateral orientations combined) decelerations: 39.4% (+/-6) versus 48.4% (+/-11). CONCLUSIONS In conclusion, at tested decelerations, under the hepatic injury threshold, cadaveric liver seemed to be subjected to higher deceleration when the trunk was decelerated in lateral than in frontal direction, without terminal impact.

Issues and challenges for pedestrian active safety systems based on real world accidents

The purpose of this study was to analyze real crashes involving pedestrians in order to evaluate the potential effectiveness of autonomous emergency braking systems (AEB) in pedestrian protection. A sample of 100 real accident cases were reconstructed providing a comprehensive set of data describing the interaction between the vehicle, the environment and the pedestrian all along the scenario of the accident. A generic AEB system based on a camera sensor for pedestrian detection was modeled in order to identify the functionality of its different attributes in the timeline of each crash scenario. These attributes were assessed to determine their impact on pedestrian safety. The influence of the detection and the activation of the AEB system were explored by varying the field of view (FOV) of the sensor and the level of deceleration. A FOV of 35° was estimated to be required to detect and react to the majority of crash scenarios. For the reaction of a system (from hazard detection to triggering the brakes), between 0.5 and 1s appears necessary.

Liver injuries in frontal crash situations a coupled numerical—experimental approach

From clinical knowledge, it has been established that hepatic traumas frequently lead to lethal injuries. In frontal or lateral crash situations, these injuries can be induced by pure deceleration effects or blunt trauma due to belt or steering wheel impact. Concerning the liver under frontal decelerations, how could one investigate organ behaviour leading to the injury mechanisms? This work couples experimental organ decelerations measurements (with 19 tests on cadaver trunks) and finite element simulation, provides a first analysis of the liver behaviour within the abdomen. It shows the influence of the liver attachment system that leads to liver trauma and also torsion effects between the two lobes of the liver. Injury mechanisms were evaluated through the four phases of the liver kinematics under frontal impact: (1) postero-anterior translation, (2) compression and sagittal rotation, (3) rotation in the transverse plane and (4) relaxation.

Anthropometric characterization of spleen in children

PurposeThis paper aims to characterize the 3D geometry of the child spleen which is still unknown.MethodsAn anthropological measurement protocol, based upon 3D modeling using spleen-computed tomography data, was set up. Characteristic measurements were defined to allow dimensions and spatial localization description from classical anatomical landmarks (11th dorsal vertebra and 10th left rib).ResultsGrowth patterns showed a global enlargement without significant changes in distance to anatomical bone points.ConclusionsThis preliminary study describes a validated measurement protocol based on 3D reconstructions and gives description of the child spleen during growth.

Relevant factors for active pedestrian safety based on 100 real accident reconstructions

Abstract The enhancement of pedestrian safety to avoid traffic accidents represents a major challenge. This study allows a better understanding of the issues in pedestrian protection. It highlights the potential of in-depth accident studies for identifying relevant crash parameters in the pedestrian active safety. A computational simulation tool was developed to reconstruct 100 pedestrian real-world crashes. Two of them are detailed to illustrate the methodology. A description of the complete sample is then presented which highlights the major factors affecting the detection of the pedestrian. These main factors concern the travel and impact speed of the vehicle, the pedestrian trajectory and his walking speed, the scene configuration with obstacles, and the weather conditions. In particular, it has been shown that 1 s before the impact, only 30% of pedestrians are located in front of the car and 90% of them are less than 20 m from the front of the car.

Acquisition and analysis of road incidents based on vehicle dynamics

Because motor vehicle crashes have decreased during the last decade in many countries in the world and are more diffuse, local authorities have difficulties to define road safety policies. An experiment with 51 cars of public fleets equipped with a specific Event Data Recorder was carried out in France during one year. The purposes of this research were to evaluate if incident data (critical driving situations) help to understand crashes, and to explore a new way for road infrastructure safety diagnosis. The analysis of 339 genuine incidents and 1237 simple events recorded illustrates the potentiality of such an experiment and provides: some insights about conditions in which incidents occur, a general overview of their distribution according to different road layouts, as well as information on the different levels of accelerations reached. It can be noticed that there is an overrepresentation of incidents in right curves compared to left curves. The simple events involving mostly the infrastructure could be used to detect road defects. Genuine incidents where the vehicle is subjected to important dynamic demands, related to potentially unsafe driving situations, can be used to improve knowledge of the motor vehicle crashes thanks to incident mechanisms analysis.