A dual carriageway (or dual-carriageway road) is a road where there is a physical barrier separating the two directions of travel. They first appeared on the British road network in the 1920s and became popular from the 1950s onward.

In the UK, although the term "dual carriageway" applies to any road with physically separated lanes, it is frequently used as a descriptive term for major routes built in this style. Such major dual carriageways usually have two lanes of traffic in each direction, with the lane nearest the centre being reserved for overtaking.