Abstract: A warning device adapted to be laid flat upon a road way produces an audible warning sound when contacted by the wheels of a moving vehicle. The device is comprised of a mat of flexible resilient material having an elongated configuration, and a series of semi-rigid apertured raised longitudinal bumps each with a plurality of segments therein forming a segmented metal bar contained therein and extending throughout the length of each bump. The bumps are spaced a few inches at most over a distance of two to three feet which allows resonant sound from the vibration of the bars and frictional interaction of short segments making up the bars to be transmitted to an overpassing vehicle traveling at high speeds. In addition, the segmented bars reinforce and extend the life of the mat.