## 4 Results
### Reconstruction of the Road Incident
Figure 15: The visualisation of the road accident resulting from damage to the suspension system in one of the cars; the speed of both being 70 km/h; (**a**) at the initial point of the accident; (**b**) moment the vehicles stopped. the other car. The effects of the collision were likely to have rendered the cars unrepairable and they would need to be scrapped. The forces acting on the cars during the collision caused the car, which was previously moving correctly, to change its path and slightly veer onto the road shoulder. That situation was sufficient to cause the pedestrian to be knocked down. The pedestrian was at such a distance that the impact force was 350 N. The value of the force was due to the earlier speed loss. As a result of knocking down, the pedestrian suffered very serious injuries that required prolonged hospital treatment. It is easy to imagine what the consequences of knocking down would have been if the pedestrian had been closer to the point where the cars collided. In this case, knocking down could even have been fatal. As scientific reports show, at speeds above 60 km/h, almost no one survives knocking down. Few pedestrians stand a chance, with pedestrians over 60 years of age suffering the most severe consequences. Cars gradually lost speed as a result of the road incident. Figure 17 shows the change in post-accident car speed as a function of the distance travelled. The car that caused the accident decreased its speed linearly to 66 km/h over 7.4 m. After exceeding that value, the car started to decelerate rapidly and, after having exceeded the eighth metre, spun and then moved backwards for another 4.4 m. The car came to a complete stop having covered 12.4 m.  
Figure 16: The location sketch showing the road accident caused by damage to the suspension system of one of the cars; the speeds of the cars involved being 70 km/h; (**a**) the initial point of the accident; (**b**) the moment the pedestrian was knocked down; (**c**) the point the vehicles stopped. Figure 17: The change in the car speed after the road incident depending on the distance covered. The car moving correctly maintained 70 km/h for 7.5 m after the collision. The car's speed was then rapidly reduced to 12.6 km. Once past that point, the car gradually slowed down until it came to a complete stop, which occurred after covering 13.3 m. That car continued to move forward over that entire road length. The examples presented in the article referred to situations where vehicles travelled at 50 and 70 km/h. If the cars had been moving at higher speeds, the consequences of the accident would have been even more drastic. It is known that kinetic energy, in a car accident, is proportional to the square of the speed. Therefore, if the speed is doubled, then the energy which needs to dissipate is quadrupled. The impact during an accident usually lasts a few microseconds. During that time, it is difficult to control the car and react accordingly. Various statistics show that a car hitting an obstacle at 90 km/h is equivalent to a fall from 30 m. If we can imagine such a situation, a collision under such conditions is equivalent to falling from the ninth or tenth floor. As mentioned previously, during a vehicle collision, especially a head-on one, a large force is released which destroys the bodywork and, thus, threatens the health of the participants in the accident. Figure 18 presents the values of the impact forces for different driving speeds. It can be seen from the data presented that the value of the forces acting on the cars during a head-on accident varies for each car and depends mainly on their mass. The case under analysis assumes two cars of different masses (in one of them, there is only the driver, and the other one has a complete set of passengers and cargo), so the speeds will add up. Therefore, the lighter car will suffer greater deceleration, which increases the risk of injury to the driver. A solution in such a case is adequate body rigidity to protect the occupants from crushing.