Vehicle Occupant Impact Severity in Relation to Real World Impact Condition

Longitudinal safety barriers are tested in order to assess the safety barriers containment capacity and the vehicle occupant impact severity. In the EN standards, the occupant impact severity is evaluated with the same test (TB11) for all the classes of barrier: a 900 kg car colliding with impact speed equal to 100 Km/h and impact angle equal to 20°. Considering that real world impact conditions may be substantially different, at least two questions arise: 1. Which is the distribution of passenger cars kinetic impact energy for different type of roads and which is the relative position of the conventional test? 2. Are the values of Acceleration Severity Index (ASI), Theoretical Head Impact Velocity (THIV) and Post-impact Head Deceleration (PHD) obtained in the conventional test TB11 representative for real world impact conditions? The “correct” answer to these questions requires a very expensive research program. This because a huge number of accident reports has to be collected and each accident events has to be reconstructed, furthermore many computer crash simulations have to be performed. In order to get a “preliminary” problem assessment, a study has been carried out performing an accident analysis and many crash simulation in different impacting conditions. The accident analysis has been carried out by the examination of 160 police run off the road accident reports on a rural dual carriageway road, integrated with the inspection of accident sites. Many accident parameters have been evaluated and distribution probabilities of impact velocity, impact angle and vehicle mass have been drawn. The real world impact conditions obtained have been used as input for the crash simulation of a passenger car against a longitudinal safety barrier. Impact simulations have been carried out by non-linear dynamic finite element analysis performed with the software LS-Dyna. The finite element model used for the vehicle is the result of an extensive modeling activity and is very capable to represent the crash dynamics and consequences. Collision outcomes in terms of THIV, PHD and ASI have been evaluated for each impact condition and, by combining the impact condition distributions with these results, the distributions of the impact severity indices have been assessed. The study carried out show that the probability of outcomes greater than the ones of the TB 11 are equal to 26% for ASI, and 34% for THIV and PHD. According to the results of the study, passenger cars crash test conditions more representative of real world impacts, on motorways and on rural dual carriageway roads, would be:  Impact speed = 130 km/h;  Impact angle = 20 degrees;  Vehicle mass = 1500 kg. Such impact conditions would represent the ninetieth percentile of cars kinetic transversal impact energy. Moreover, with reference to the rigid wall fixed to the ground used in the simulations, they give rise to ASI, THIV and PHD values more severe than eighty-five percent of real world run off the road accidents. The previous results show that the conditions proposed by the standard could be not conservative in Italy. They have to be intended, however, as preliminaries and stressing the need of a more in depth research program.