Warning signs or flashing lights. If you see or hear emergency or incident support vehicles in the distance, be aware there may be an incident ahead (see Rule 219). Police Officers and Highways Agency Traffic Officers may be required to work in the carriageway, for example dealing with debris, collisions or conducting rolling road blocks. Police officers will use rear-facing flashing red and blue lights and HA Traffic Officers will use rear-facing flashing red and amber lights in these situations. Watch out for such signals, slow down and be prepared to stop. You MUST follow any directions given by Police officers or Traffic officers as to whether you can safely pass the incident or blockage.