Methods for the measurement of the object spacing distance or separation of objects are increasingly utilized in obstacle warning systems for motor vehicles, in order to warn the drivers of the motor vehicles of sources of danger on the roadway. It would be sensible or suitable in such a system, to take into account also the relative speed of objects approaching the motor vehicle. The new method shall enable the determination of the relative speed of an object in a simple manner and provide exact measurement results. In the new measurement method, the object separation is cyclically determined respectively after expiration of a prescribed cycle period. Furthermore, the number of the cycles is determined, within which the object separation changes so far that a prescribed separation band is completely traversed. The relative speed of the object is then calculated from the difference between the object separation determined before the entry into the separation band and the object separation determined after the exit out of the separation band, and from the determined number of cycles. Pre-crash sensing.