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.

A dual carriageway is defined as a road that has a central reservation separating lanes of traffic. The reservation can be anything other than a pedestrian refuge.

A dual carriageway road has two separate paved surfaces side-by-side, with some sort of physical divider or barrier between them.