Load and Impact Conditions for Head Injuries in Car-to-Pedestrian and Car-to-Cyclist Accidents – A Comparison of Real Accidents and Simulations Yong Chen 1 , Jikuang Yang 1, 2 , Dietmar Otte 3 1 Research Center of Vehicle and Traffic Safety, State Key Laboratory of Advanced Design and Manufacture for Vehicle Body, Hunan University, 410082, China; 2 Department of Applied Mechanics, Chalmers University of Technology, Sweden; 3 Accident Research Unit, Medical University of Hannover, 30625, Germany Abstract: Pedestrian and cyclist are the most vulnerable road users in traffic crashes. One important aspect of this study was the comparable analysis of the exact impact configuration and the resulting injury patterns of pedestrians and cyclists in view of epidemiology. The secondary aim was assessment of head injury risks and kinematics of adult pedestrian and cyclists in primary and secondary impacts and to correlate the injuries related to physical parameters like HIC value, 3ms linear acceleration, and discuss the technical parameter with injuries observed in real-world accidents based documented real accidents of GIDAS and explains the head injuries by simulated load and impact conditions based on PC-Crash and MADYMO. A subsample of n=402 pedestrians and n=940 bicyclists from GIDAS database, Germany was used for pre- selection, from which 22 pedestrian and 18 cyclist accidents were selected for reconstruction by initially using PC-Crash to calculate impact conditions, such as vehicle impact velocity, vehicle kinematic sequence and throw out distance. The impact conditions then were employed to identify the initial conditions in simulation of MADYMO reconstruction. The results show that cyclists always suffer lower injury outcomes for the same accident severity. Differences in HIC, head relative impact velocity, 3ms linear contiguous acceleration, maximum angular velocity and acceleration, contact force, throwing distance and head contact timing are shown. The differences of landing conditions in secondary impacts of pedestrians and cyclists are also identified. Injury risk curves were generated by logistic regression model for each predicting physical parameters. Keywords: Pedestrian and cyclist; Accident reconstruction; Head kinematics and injury; Comparison study INTRODUCTION In the European Union (EU) 8,000 unprotected traffic participants, pedestrians and cyclists die annually, 300,000 are severely injured and 1.4 million are slightly injured annually in the course of traffic accidents [1]. Within the EU countries, the relative frequency of the pedestrian fatalities varies remarkably from 14% in Sweden to 32% in UK. The pedestrian fatalities in USA are about 5,000 and 3,000 in Japan each year. In China about 25,000 pedestrians are killed in the traffic accidents each year [2]. According to the statistical data, of total the traffic fatalities about 60% were pedestrians, cyclists and motorcyclists during the year 2000 to 2005[3] in China. The vulnerable road users expose a high risk in traffic accidents [4] due to that they participate in public traffic as unprotected persons. During the last 20 years pedestrian safety has been widely studied and pedestrian protection becomes of increasing concern of the world, especially in the EU. Component subsystem tests for cars proposed by the European Enhanced Vehicle-safety Committee (EEVC/WG10 and WG17) were approved to assess pedestrian protection. The question is now to what extent results for the injury situation based on data of pedestrian accidents also apply to bicyclists, who also are to be protected by this directive. The latter are, however, by using self-protection measures such as a bicycle helmet and the proper motion relative to the motorcar as well as because of the coupled mass system driver- bicycle on the one hand rather similar to vehicle /vehicle collisions, on the other hand also comparable as far as the occurring kinematics are concerned. Thus the question arises whether in consideration of the injury situation and the severity of the accident the demands on the test conditions can also be valued analogously. Bicycles generally do not have a standardized structure and there is no conformity criterion for the material used, design and construction methods. Hence generic safety standard for bicycle riders have been very difficult to formulate and are not standardized yet. In-depth accident investigation and accidents reconstruction is regarded as one of the efficient means to understand the injury mechanisms in pedestrian and cyclist accidents. Previous studies about pedestrian and cyclist accidents were mainly focused on the relationship between injury descriptions, impact velocities,