Some Remarks on Automatic Braking System Related to Pedestrian Safety

Collision avoidance systems (CAS) have greatly increased in automotive market since they have proven to be effective in reducing head-on crashes. An interesting application of these system has been used in pedestrian safety by means of automatic braking systems. The key operating parameter for these advanced emergency braking system is based on the Time-To-Collision (TTC) concept that, in turn, it is strongly affected by the actuated overall mean deceleration that on dry pavement surface is about 8 to 10 m/s2. However, since the corresponding stopping distance is mainly influenced by tire-road friction level, on wet pavement surfaces much lower deceleration values can be reached thus implying a dramatic recalibration of decision rules governing the operating conditions of the system. In this paper a methodology to evaluate the mean deceleration useful to estimate optimal TTC values on wet pavement surface is presented as far as an advanced emergency braking system designed to reduce the risk in pedestrian vehicle crashes is concerned. By making use of a correlation model between pavement surface characteristics and tire performance, this latter expressed by means of a conventional tire labeling value, according to current EU legislations, stopping distance and corresponding mean deceleration value can be derived on a stochastic basis. An example application is finally presented to illustrate the methodology developed.