What does a flashing amber beacon mean when it’s on a moving vehicle?
Different coloured beacons warn of different types of vehicle needing special attention. Blue beacons are used on emergency vehicles that need priority. Green beacons are found on doctors’ cars. Amber beacons generally denote slower moving vehicles, which are often large. These vehicles are usually involved in road maintenance or local amenities and make frequent stops.
Flashing amber beacons on moving vehicles
The question above relates to rule 225 from the UK Highway Code which states:
Vehicles with flashing amber beacons. These warn of a 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).
In rule 220 we see another instance of where flashing amber beacons may be used on moving vehicles, but again these are slow moving vehicles:
Powered vehicles used by disabled people. These small vehicles travel at a maximum speed of 8 mph (12 km/h). On a dual carriageway where the speed limit exceeds 50 mph (80 km/h) they MUST have a flashing amber beacon, but on other roads you may not have that advance warning (see Rules 36 to 46 inclusive).