What is another word for underground railways?
Pronunciation: [ˌʌndəɡɹˈa͡ʊnd ɹˈe͡ɪlwe͡ɪz] (IPA) 
Underground railways refer to the network of railways that run underneath the city. Some popular synonyms for underground railways include subways, tube, metro, rapid transit, or mass transit system. The word subway is most commonly used in North America while the term metro is popularly used in Europe, particularly in France, Spain, and Portugal. The London Underground or the Tube is the oldest and most famous underground railway system in the world and is often considered as a synonym for this type of transport. The term rapid transit system is widely used in Canada and the United States and refers to a high-speed rail service that can run both underground and on elevated tracks.
