Construction Warning (CW20 thru CW22) signs: Temporary traffic control zone signs where road conditions are changed because of a work zone. CW20 signs alert motorists of ramp, road, or land closures, detours, or flaggers ahead. CW21 signs warn motorists of road work ahead, and the presence of work crews and machinery. CW22 signs indicate a blasting zone ahead. Prior to applying for a permit from DOT, fax (808-842-1233) or deliver drawings of your work zone to our traffic control division for sign compliance recommendations.