Discussed here is the influence of the precollision speed, or the speed right before the driver attempts any preventive operations such as braking.
Figure 10 shows the precollision speed and the occurrence rate of vehicle rollover in accidents caused by a single vehicle. It is clear that the higher the precollision speed is, the more frequently vehicle rollover occurs-that is, a higher speed could bring unstable conditions where a vehicle would skid sideways or run off the road. In the case of accidents caused by a single vehicle, overturned automobiles are most frequently seen on "expressways, etc."
(Fig. 11).
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| Figure 12 shows the precollision speed and the occurrence rate of vehicle rollover of the impacted vehicles. In the case of accidents involving two vehicles, higher precollision speed will similarly cause more rollovers. On the other hand, vehicle rollover occurs even at speeds of less than 20 km/h. In this case, the speed of the colliding vehicles is high. Therefore, even if the speed of a car is low, there is a risk of turning over in the event of collision, because the speed of the other vehicle may be high.
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