Integrated pedestrian safety assessment methodology

Licentiatavhandling, 2014

Pedestrian fatalities and injuries are a concern in many regions. Passive safety assessment is well established, and additional active safety assessment has recently emerged. However, assessment methods reflecting on the interaction between active and passive safety do not exist in regulatory or consumer testing. An integrated safety assessment that takes consideration to the information gained by active safety evaluation and modifies the passive safety assessment accordingly is needed to reduce pedestrian casualties effectively and efficiently. Such an assessment can guide the development and proliferation of vehicles offering the greatest benefit in terms of total safety offered. The goal of this thesis is to contribute to the development of an integrated pedestrian safety assessment methodology. Firstly, conceptual work identifies key issues and a way forward for the assessment of True Positive performance, which is predicted injury reduction in test conditions in which safety systems are to be activated. Secondly, False Positive test procedures are considered to provide guidance on balancing between True Positive performance and False Positive driver annoyance (activation of automatic emergency braking or forward collision warnings in test conditions in which safety systems are not meant to activate leading to driver mistrust and switched-of systems). To do so, driver comfort zone boundaries for pedestrian crossing situations are quantified indicating the transition point from normal situations to uncomfortable driving situations in which the driver will take corrective action. This data can be used to differentiate between desired and undesired False Positive activation, which in turn can help in designing False Positive test procedures. A concept for the development of an integrated pedestrian safety assessment methodology is presented in Paper I. Further work is needed to collect data to facilitate the design of a usable and accurate assessment method from this concept. Comfort zone boundaries for pedestrian crossing situations were quantified in Papers II and III. Time-To-Collision (TTC) had comparably low variation in the driver population in two complimentary studies on both a test track and in a driving simulator. The comfort zone boundary TTC was independent of the car’s travelling speed but depended on pedestrian crossing speed. The 90 percentile value for TTC at the comfort zone boundary for 1 m/s pedestrian speed was 2.5 s in Paper II and 2.6 s in Paper III. The value for pedestrian speed of 2 m/s was 2.2 s TTC identified in Paper III. The methodology as suggested in this thesis relies on the testing of active safety systems in representative scenarios, and testing of passive safety with impactor tests. Thus, any limitations with the test procedures for active and passive safety, such as unrealistic reflectivity of test targets or lack of biofidelity of impactors, will have its impact on the integrated methodology.