# The Contact Phase in Vehicle-Pedestrian Accident Reconstruction
## 3 Research Methods and Models
These were modeled by accepting the following initial data:  
* The types of vehicles involved in the collision were the following: compact class-CC, super-mini class-SMC, executive class-EC and compact SUV-CSUV;
* Vehicle initial speed was 5, 10, 15 and 20 m/s;
* Vehicle deceleration during impact was 0, 2.5, 5 and 7.5 m/s2;
* Pedestrian walking perpendicular to vehicle direction at 1.4 m/s;
* The coefficient of friction between vehicle and pedestrian is 0.2;
* The moment when the contact force between the body segment (head/torso) and the vehicle is zero is considered to be the moment of separation from the vehicle, as illustrated in Figure 6.  
Various areas of the body come into contact with the vehicle during the impact, but only the lower limbs, chest and head were considered in our analyses. In [27], various body postures were defined while walking based on previous studies that state that the pedestrian's posture at the moment of impact influences the kinematics of the impact between the car and the pedestrian. Using MADYMO model, [PERSON] et al. [28] selected six initial stance configurations from the gait cycle defined in [20]. In the simulations performed by the authors, impacts were performed with the pedestrian moving transversally (walking) to the vehicle at a speed of 1.4 m/s. A summary of the simulations performed is given in Table 1.  
Figure 5: Pedestrian positions at the time of the impact. Figure 6: Example of pedestrian contact forces during impact with car. [PERSON] et al. [29] used MADYMO ellipsoid multibody pedestrian model and real test with cadavers, performed over a speed range of 20-30 kph and with three different vehicle types and pedestrian sizes, and found a good capacity to predict vehicle contact times. In [30], the MADYMO ellipsoid multibody pedestrian model is also used. Each model consists of 52 rigid bodies with an outer surface described by 64 ellipsoids. The MADYMO models were used to study accident reconstructions, particularly those involving vulnerable road users [31; 32; 33]. [PERSON] [34] carried out an extensive study on the friction coefficients that occur in traffic accidents involving pedestrians. A non-linear frictional contact model in vehicle-pedestrian accidents was considered in [35]. The study based on their model indicates that the pedestrian-ground friction coefficient is not consistent. The relationship between the friction force and the contact pressure is non-linear. In [36], the authors chose to use in their research the friction coefficients between the pedestrian and the ground with a value of 0.6, and between the pedestrian and the vehicle with a value of 0.3. The dummy used had the characteristics shown in Table 2 during simulations. The moments in the main joints of the body (torso, neck, knees, and ankles) were adapted to mimic the human body as closely as possible. Studies of moments in various body joints in different postures were carried out for the knee [37], for the walking posture [38], including the hip, knees and ankles, and for the neck [39]. Body data are adjusted according to the report \"International Data on Anthropometry\" by [PERSON], [PERSON] and [PERSON], published by the Federal Institute for Occupational Safety and Health, Dortmund, Federal Republic of Germany and a study made by various scientists in Slovakia [22], as shown in Table 2.  
A summary of the performed simulations is given in Table 3. \begin{table}
\begin{tabular}{l l l} \hline \hline \multirow{2}{*}{Pedestrian male adult} & Age & 18 years \\  & Mass & 75 kg \\ \cline{2-3}  & Height & 1.75 m \\  & No of body elements & 20 \\  & Friction coefficient with car & 0.20 \\ \cline{2-3}  & Friction coefficient with ground & 0.60 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Pedestrian default characteristics data.