In the United Kingdom, cars may travel at a maximum of 70 mph on dual carriageways when no lower limit is posted.
This is the national speed limit for cars and motorcycles on both motorways and dual carriageways. A dual carriageway is defined by a central physical separation between opposing traffic flows, not simply by the number of lanes.
The limit can be reduced by signs, including temporary limits at roadworks or permanent limits near urban areas and junctions. Drivers must also obey lower limits applying to particular vehicle classes, such as heavy goods vehicles.
A common mix-up is assuming every road with two lanes in each direction is a dual carriageway. The deciding feature is the central reservation or other physical division. The 70 mph limit is also different from the default 60 mph limit for cars on single carriageways.