1. A method of operating a driver assistance system of a vehicle travelling on a roadway comprising: operating a vehicle-mounted sensor system to determine location and movement variables of an object, the sensor system having two detection zones separated by a gap; assigning a movement model to the object; updating the movement model using the location and movement variables from the sensor system while the object remains in one of the detection zones; when the object moves out of the detection zones, assessing a probability that the object is in the gap using the movement model and using roadway features by which the object may exit the roadway; and affecting a vehicle system in response to the probability.