Assessment of Active and Passive Technical Measures for Pedestrian Protection at the Vehicle Front

Structural improvements at the vehicle front are state of the art in the field of pedestrian safety today. But due to raising requirements further measures will be needed. The active bonnet for example is the first deployable system that has entered the market. Other passive safety systems, like the windscreen airbag, are part of current research. This applies also to systems of active safety such as autonomous braking. Hereby the collision speed can be reduced or an accident can be even avoided. To assess and compare the safety potential of active and passive pedestrian safety measures on one scale, an assessment procedure has been developed and applied to various measures and vehicle fronts. An important characteristic of the assessment procedure is its modular design, combining structural characteristics of a vehicle front with accident kinematics and accident research data. Each module can be enhanced or substituted independently. The assessment procedure uses the vehicle model specific Euro NCAP results and adapts the HIC values to the real accident kinematics derived from numerical simulations. Since the kinematics strongly depend on the front design of a car, a categorization has been developed. For each vehicle class respective simulation data is available. Kinematics parameters are the head impact velocity, impact angle and impact probability determined for the particular wrap-around-distance zones of the vehicle front. The assessment procedure primarily provides an index value which indicates the risk for an AIS3+ head injury due to the primary impact at a collision speed of 40 km/h. It is calculated for children and adults by an injury risk curve. In addition the dependency of this index value from the collision speed is determined based on corresponding simulation data. Beside the head loading also the leg loading is assessed. This is carried out by a simplified index calculation. The secondary impact is evaluated qualitatively. The assessment procedure brings the evaluation of active and passive safety together. Index values have been calculated for good as well as poor rated vehicles within Euro NCAP and under consideration of varying additional safety systems. It could be shown that the benefit of today’s measures applied to the vehicle front is limited. Legal test requirements and consumer ratings insufficiently reflect the vehicle-class-specific relevance of particular front areas. Simulation data points out the A-pillars and the lower windscreen area, which need to be addressed by technical measures. Furthermore there is no “one fits all” measure which performs on the same positive level at all vehicle fronts and for all pedestrian sizes. Therefore measures have to be selected and adjusted for each car front. A windscreen airbag is able to improve adult pedestrian safety significantly. Children however profit more by emergency brake systems with pedestrian detection due to the limited safety potential of an active bonnet. Consequently, future cars should offer both adequate passive pedestrian protection and additional active safety systems. The benefit of relevant passive safety systems as well as reductions in collision speed has been demonstrated by Polar-II dummy tests with an experimental vehicle.