1. A method for preventing collisions of vehicles in oncoming and turning traffic, in which the surroundings of a vehicle and motion parameters of a vehicle are ascertained by means of sensors, wherein: from output signals of the sensors ( 2. 1 , 2. 2 , 2. 3 , 2. 4 , 2. 5 ), a driver attentiveness criterion (A), which is a measure of the capability of a driver of the vehicle to react to a turning situation, and a collision risk criterion (K) are derived; from a combination of the driver attentiveness criterion (A) and the collision risk criterion (K), a risk level is ascertained; and as a function of the risk level ascertained, predeterminable steps for reducing a collision risk are initiated.