The aim of the invention is to monitor the travel way of a road processing machine that drives on a basic surface as well as the working height of a working part which is disposed thereon in a vertically adjustable manner. Said aim is achieved by detecting the three-dimensional position of a positional element, determining a direction of travel from at least two three-dimensional positions, and determining the working height of the working part. The determined direction of travel is compared to a setpoint direction while the working height is compared to a setpoint height. The positional element is placed in a position that is at a horizontal distance from the working part.