Sánchez 1 ESTIMATION OF THE HEAD INJURY SEVERITY USING THE HEAD IMPACT SPEED BASED ON REAL PEDESTRIAN COLLISIONS

A vehicle-pedestrian impact is a complex phenomenon in which a large number of variables take part simultaneously determining the injury severity of the pedestrian. Statistical techniques were applied to data from 43 pedestrian accidents that occurred in Madrid, following a similar approach to the one applied in previous publications from authors. In this case, however, the general research objective has been oriented to model the pedestrian head injury severity as a function of the head impact speed instead of the pedestrian impact speed, and a reduced number of independent variables that affect the pedestrian impact kinematic. In previous studies authors have estimated the head injury severity using the pedestrian impact speed. The results of this paper are focused on analyzing variations on head injury severity estimations considering both the head impact speed and the pedestrian impact speed (vehicle speed); and the pedestrian impact kinematic variables influencing these variations. As a specific objective of this research the previous methodology has been applied to review thoroughly the results about the potential influence of several autonomous emergency braking systems (AEB) estimated in the previous paper of authors. The vehicle-pedestrian collisions have been in-depth investigated following a common methodology, including on the spot data collection, analysis and reconstruction to estimate the pedestrian impact speed, the head impact speed and the pedestrian kinematics. Every single case has been virtual simulated using the PC-Crash® software. The first is a reconstruction of the real accident and the following are simulations in which the operation of AEB systems are emulated. For this paper, the methodology used to estimate the head injury severity has been described previously. In summary, from the location of head contact, the collision speed and vehicle characteristics, the probability of suffering a severe (AIS3+) head injury (ISP, Injury Severity Probability) is obtained. The findings show that the head impact speed is lower than the pedestrian impact speed in the 79% of the cases. Otherwise the Injury Severity Probability considering the head impact speed is lower than the IPS estimated with the pedestrian impact speed in the 68% of the cases due to the influence of the impact area stiffness. In some cases a low reduction of the pedestrian impact speed due to the AEB systems would increase the estimated ISP (ineffective AEB cases). The interaction among collision speed, vehicle frontal design and pedestrian parameters is more relevant for the severity of the pedestrian head impact than the speed by itself. Considering the head impact speed for the ISP estimation, the number of ineffective AEB cases increases. Limitations of this research are the sample size (only one city and frontal collisions) and that no unhurt accidents have been included. The injury severity assessment within this study only considers head impacts to the front surface of the vehicle, injuries provoked by subsequent impacts were not taken into account. Hence it can be an interesting subject for further research.