# The Contact Phase in Vehicle-Pedestrian Accident Reconstruction
## 3 Research Methods and Models
Custom vehicle multibodies can be specified for interaction with other multibodies [22]. Properties for stiffness-based impacts can be also specified as follows:  
* Friction--This is the coefficient of friction for the vehicle body. * Restitution--This is the coefficient of restitution for vehicle impacts. If the stiffness-based impact model is used, only one restitution coefficient for all concerned vehicles should be used. * Stiffness--This is expressed as a deformation distance. For passenger cars, the specified stiffness is for the lower part of the vehicle body only. For the roof, one quarter of the specified stiffness is used. Multibody forensic models available in reconstruction software were often validated by comparing body motion with video data either from dummy crash tests or CCTV recordings [21]. In [24; 25], the authors used camera images from real accidents involving pedestrians as a technique for accident analysis. The videos were recorded over time, with different high-speed cameras at the rate of 500 or 1000 fps, with image resolution of 845 \(\times\) 480 and 640 \(\times\) 480 pixels. The position of the cameras was fixed; the filming was carried out in open spaces with strong sunlight or in laboratory with special lighting facilities. The collision speed and the vehicles deceleration were determined with datalogger-type measuring equipment that includes accelerometers. To establish the travel distance, we used photogrammetric techniques, with at least one known dimension. \begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline
**Vehicle** & **Mass** & **Height** & **a** & **b** & **c** & **d** & **1** & **2** & **3** & **4** \\
**Type** & **[kg]** & **[m]** & **[m]** & **[m]** & **[m]** & **[m]** & **[m]** & **[m]** & **[m]** & **[m]** \\ \hline SM-1 & 795 & 1.465 & 0.050 & 0.058 & 0.871 & 0.498 & 0.350 & 0.500 & 0.837 & 0.942 \\ \hline SM2 & 854 & 1.489 & 0.050 & 0.052 & 0.904 & 0.517 & 0.350 & 0.500 & 0.851 & 0.957 \\ \hline CC-1 & 1390 & 1.410 & 0.050 & 0.065 & 1.142 & 0.653 & 0.350 & 0.500 & 0.806 & 0.906 \\ \hline CC-2 & 1180 & 1.420 & 0.050 & 0.064 & 1.124 & 0.642 & 0.350 & 0.500 & 0.811 & 0.913 \\ \hline CC-3 & 1395 & 1.462 & 0.050 & 0.067 & 1.167 & 0.667 & 0.350 & 0.500 & 0.835 & 0.940 \\ \hline CC-4 & 1025 & 1.535 & 0.050 & 0.063 & 1.096 & 0.626 & 0.350 & 0.500 & 0.877 & 0.987 \\ \hline CSUV-1 & 1585 & 1.700 & 0.050 & 0.065 & 1.130 & 0.646 & 0.350 & 0.500 & 0.971 & 1.093 \\ \hline CSUV-2 & 1280 & 1.630 & 0.050 & 0.063 & 1.102 & 0.630 & 0.350 & 0.500 & 0.931 & 1.048 \\ \hline EC-1 & 2135 & 1.480 & 0.050 & 0.076 & 1.335 & 0.763 & 0.350 & 0.500 & 0.846 & 0.951 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Vehicle characteristics; source: PC-CRASH. Figure 4: Vehicle geometrical characteristics, source [22]. The simulations analyzed pedestrians in a walking posture, crossing in front of a vehicle, perpendicular to their direction of travel. These types of accidents were also revealed in [26]. The authors showed that when focusing on the distribution ratio of the cases when pedestrians were crossing the roads in front of the forward moving cars, these were 67% (fatal) in daytime and 78% at night-time. Two different cases of first contact in the leg area were analyzed, namely when the body weight is taken on the front leg (P1) and when it is taken on the rear leg during walking (P2), as shown in Figure 5.  
The simulation was carried out in 3D. During the simulation, collisions occurred between the car and the pedestrian at different vehicle speeds.