Priorities and Potential of Pedestrian Protection: Accident data, Experimental tests and Numerical Simulations of Car-to-Pedestrian Impacts

Pedestrian disability and fatality as a consequence of ar crashes is a large global health problem. To introduce maximally effective ca r-b sed countermeasures it is important to understand which injuries are most com m n and from which car parts they originate. It is also important to focus on th e most severe injuries resulting in disability or death. The aim of this thesis was the refore to determine priorities for and evaluate the potential of car-mounted safety system designed to mitigate severe upper-body injuries (including disability and fatal ity) of pedestrians in car crashes. Accident data was collected from two areas; severe (AIS3+) accidents in Dresden/Hannover in Germany and fatal accidents in Sweden. For the surviving pedestrians an estimate of long-term injury was per formed using accident dataderived risk matrices of permanent injury. Results showed that 31% would sustain a permanent impairment of some kind and 5% would sust ain a more severe impairment, where the head was most susceptible to s vere impairment. The car front frequently caused leg injuries, which is addr essed in current regulations. However, current legal tests do not address the mos t common upper-body injury source, the windshield, which was found to be the d ominating cause of head injuries. Chest injuries, frequently caused by both the hood and windshield areas in the severe and fatal crashes in this thesis, are also unaddres sed in legal tests. Children are most commonly head-injured from the hood area, which is addressed in current regulations. Further, regulations do not fully cons ider brain injury with the current head test methods. Therefore, in this thesis focus was on upper-body injury/source combinations not addressed in the regulations, that is, the head-to-windshield area and chest-to-hood/windshield areas, and the evaluat ion of brain injury in hood and windshield impacts. Experimental head-to-hood component tests with succ eeding brain simulations were performed to evaluate the influence of the under-ho od distance and head impact speed. A hood designed to minimize linear head load ing to acceptable injury levels was also found effective in reducing combined linea r/rotational brain loading. Further, in full-scale car-to-pedestrian finite ele ment simulations both a braking and deployable system alone proved efficient in reducin g head and chest loading, and an integrated countermeasure of combining the two syst em proved to increase the protection potential. While current pedestrian countermeasures focus on t he head-to-hood impact, this thesis recommends extending countermeasures to the l wer part of the windshield and the A-pillars, and adding brain and chest injur y assessment for both hood and windshield areas to effectively minimize disabling and fatal injuries. Since head impact location and head impact speed is dependent on the car design, the introduction of full-scale simulations in the test methods to determine impact conditions for experimental component tests is reco mmended. If the deployable countermeasures are combined with autonomous brakin g in an integrated system the most effective system is achieved. Auto-brake syste m should, in high speed impacts, aim to reduce speeds to where the secondar y countermeasures can effectively mitigate injury. Future pedestrian test methods should therefore evaluate how primary and secondary countermeasures interact. LIST OF PUBLICATIONS This thesis is based on the following papers, which will be referred to in the text by their roman numerals. I. Fredriksson R, Rosén E and Kullgren A. Priorities of pedestrian protection – A real-life study of severe injuries and car sour ces. Accident Analysis & Prevention, Vol. 42 (6), pp. 1672-1681, 2010. 1 II. Fredriksson R, Zhang L, Boström O and Yang K. Influence of impact speed on head and brain injury outcome in vulnerable road user impacts to the car hood. Stapp Car Crash Journal, Vol. 51, pp. 155-167, 20 07. III. Fredriksson R, Shin J and Untaroiu C. Potential of Pedestrian Protection Systems – A Parameter Study Using Finite Element Mo dels of Pedestrian Dummy and Generic Passenger Vehicles . Accepted for publication in Traffic Injury Prevention, 2011. 3 1 Fredriksson designed the study with assistance from Rosén. Rosén performed the statistical analyses and Fredriksson performed the detailed cas e analyses. Kullgren assisted with design and analysis of long-term injury evaluation. The paper was jointly written by Fredriksson and Rosén. 2 Fredriksson and Boström designed the study wit h assistance from Zhang and Yang. Fredriksson performed mechanical tests, and Zhang performed the numerical simulations. Fredriksson performed the analysis with assistance from Zhang and Boström . Fredriksson, primarily, and Zhang were the