AAATHE slow-moving or stationary vehicle (such as a Traffic Officer vehicle,  salt spreader, snow plough or recovery vehicle) or abnormal loads,  so approach with caution. On unrestricted dual carriageways,  motor vehicles first used on or after 1 January 1947 with a  maximum speed of 25 mph (40 km/h) or less (such as  tractors) MUST   use a flashing amber beacon (also see Rule 220  above). Law RVLR 1989, reg 17  highwaycodeuk.co.uk 117 