A method and a device for generating a signal which indicates the imminent formation of slipperiness on a roadway (2) before this arises on the roadway, wherein radiation reflected from the roadway, or from a point adjacent to the roadway, is evaluated, which radiation emanates from at least one reference surface (11) arranged in or on the roadway or the adjacent point, which reference surface is formed by a material different from the roadway covering material. The reference surface is selected from a material on which slipperiness is formed earlier than on the road surface material. The signal (13) is emitted when the evaluation shows that slipperiness has formed on the reference surface (11).