A method for controlling the motion of a mobile warning triangle for suitable placement on a roadway acquires information as to color of the lane markings detected by a sensor. When the mobile warning triangle is first placed on the roadway, the sensor is preset in position to detect the lane marking. White or yellow color information of the lane marking or of the black-colored roadway are detected or are not detected by the sensor, and deviations from a required path are recognized when different colors are received in certain combinations by the sensor. If no deviation is recognized in the colors, the mobile warning triangle continues moving forward. If a deviation in colors is recognized, the mobile warning triangle is controlled to hunt to the left and right through one or more predetermined angles to try to detect or redetect the lane marking.