Abstract: A portable apparatus for warning drivers of temporary and/or hazardous road conditions ahead comprising a portable flat mat of resilient material which is either removably or permanently secured to the road surface in or near the path of an oncoming vehicle, and which has a plurality of equidistantly sapced slotted openings formed therein each of a size to completely, momentarily receive at least one of the front tires of the vehicle. When the said front or any other tire runs over said slotted openings, an audible and mechanical rumbling of the vehicle is set up thereby warning and physically alerting the driver of a road condition ahead which requires special attention.