A portable highway warning device includes any number of elongated rumble strips each fabricated of a suitable flexible polymeric material. Embedded within each rumble strip are a plurality of laterally spaced metal plates or bars to provide ballast to each rumble strip. The metal plates or bars run transversely across the width of each rumble strip with sufficient spacing therebetween to permit each rumble strip to be rolled up lengthwise from end to end when not in use.
