There are three types of expressway in the UK.
- Motorways: restricted D2/D3/D4 roads with grade-separated junctions (GSJs) and a "hard shoulder", i.e. a spare lane to stop in in an emergency. They have "M" numbers, blue signs, and are shown in blue on maps. The usual speed limit for cars is 70 mph. See CBRD's motorway database.
- Free-flow dual-carriageways: restricted D2/D3 roads with GSJs. These roads look and feel like motorways but have "A" numbers, green signs, and are shown in green on maps. (Green is the usual colour for Britain's major roads.) A database of these non-motorway expressways will be built up in due course.
- Urban expressways: S2/D2 roads with at-grade junctions (i.e. roundabouts and traffic lights) which serve as the main traffic routes in cities. The speed limit is likely to be 40 mph.
The last type, although they're often called expressways, don't really fit this wiki's definition of an expressway, and information about them will be found at the UK Roads wiki.
Terminology:
"S" stands for single carriageway; "D" for dual carriageway. Examples:
S1: an undivided road with one lane in each direction
D2: a divided road with two lanes in each direction