Collision avoidance actions in a road vehicle are controlled based on a computed probability density of future positions of the vehicle. A preliminary probability density (32) is computed by means of a mechanical model by extrapolation from the detected state of the vehicle, including at least its detected position(31). Map data is used to define different regions in an area that contains the road, such as a first region that comprises a road part for traffic that moves in the direction of travel of the vehicle, a second region that comprises a road part for traffic in the opposite direction and a third region bordering on the road. The regions are used to obtain a correction factor of the computed probability density function in the first region (33). The correction factor is computed dependent on the aggregates of the probability density function in respective ones of the regions. In this way it is possible to compensate for errors that result from extrapolations that misinterpret swerving motion that suggest that the vehicle will move of the road, but are automatically corrected by the driver.