Abstract
This paper describes the main findings of a coordinated study performed by INSIA-UPM aimed to assess the potential influence of an automatic brake system in vehicle-pedestrian collisions through reconstruction of real-world accidents occurred in the city of Madrid (Spain). The automatic brake system emulated in this paper through computer simulations is based on the DaimlerChrysler’s PROTECTOR system.
Data of 50 frontal vehicle-pedestrian collisions occurred in the city of Madrid between 2002 and 2006 were collected. Every single case has been virtual simulated twice using PC-Crash® software: the first is a reconstruction of the real accident and the second is a simulation in which the operation of the automatic brake system is emulated modifying the collision parameters and its potential consequences. The benefit is assessed in terms of both collision speed and Injury Severity Probability (ISP) by comparing the reduction of their values from the real conditions to the virtual simulations. The pedestrian ISP was estimated, depending on the collision speed and the head impact point, using a specific application to calculate its value based on the results of head form impact laboratory tests.
The findings show that in several cases the collision could be avoided by implementing the automatic brake system; and it would reduce their consequences in terms of the estimated ISP. In 53% of the cases of the studied sample the percentage of the speed reduction achieved is more than 90%; and in 67% of the cases the percentage of the ISP reduction achieved is more than 80%. It was also found that in few cases a low reduction of the collision speed would increase the head injury severity.
Further research should include injury information and/or estimation (HIC). Other limitations are the sample size (only one city and frontal collisions) and 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.
The paper offers a new approach in the field of the assessment of automatic brake systems; it is based on accurate reconstructions, highly detailed parameters; the behavior of the system is simulated according to design parameters.
Multi-disciplinary approaches such as this study make the identification of critical parameters easier and simplify the development of practical solutions by quantifying their potential impact on future actions to improve pedestrian safety. The gathered information has been used for the evaluation of the effectiveness of the automatic brake system (PROTECTOR). The performance of these systems has been simulated in the reconstructions, so it was possible to analyse their capacity for severity reduction in pedestrian accidents or even its avoidance.
The analysed system proved to be efficient for reducing severity of pedestrian accidents in most of the studied cases. The findings show that a part of the collisions could have been avoided by implementing this system; and in most of other cases their consequences would have been reduced in terms of the estimated ISP. The interaction between collision speed, vehicle frontal design and pedestrian parameters –height, weight, speed – is more relevant for the severity of the pedestrian head impact than the speed by itself, because it determines the head trajectory, acceleration and impact point. Thus, these primary safety systems should be combined with other secondary safety devices, such as the pop-up bonnet or the windscreen airbag.
KEYWORDS – Pedestrian safety, automatic brake system, on the spot accident investigation, injury severity probability, accident reconstruction