Dual carriageway and Viaduct

Dual carriageway noun - A highway divided down the middle by a barrier that separates traffic going in different directions.

Viaduct and dual carriageway are semantically related. In some cases you can use "Viaduct" instead a noun phrase "Dual carriageway".

Viaduct noun - Bridge consisting of a series of arches supported by piers used to carry a road (or railroad) over a valley.

Dual carriageway and viaduct are semantically related. Sometimes you can use "Dual carriageway" instead a noun "Viaduct".