Explanation

"Vehicles carrying loads between 4.3 metres (14 feet 1 inch) and 5 metres (16 feet 6 inches) wide are subject to lower speed limits. The limit depends on the type of road. On a motorway it's 40 mph (64 km/h), on a dual carriageway it's 35 mph (56 km/h), and on all other roads it's 30 mph (48 km/h)."