Nah Jazzo - it's what Hev said.....

To my mind, a "carriageway" is not a highway per se - though it may be part of a highway. A dual carriageway is two separate roads carrying traffic in opposite directions.

IMHO, "motorway" is synonymous with "highway", "freeway" & "expressway" - ie, the sum total of all the carriageways.

stales