1. A method of estimating a time-to-collision (TTC) of a vehicle with an object comprising the step of: (a) acquiring a plurality of images of the object at known time intervals between the times at which the images of the plurality of images are acquired; and (b) determining the time-to-collision (TTC) solely from information derived from the images and the time intervals, wherein said determining the TTC is based on a relative velocity and relative acceleration between the vehicle and the object.