UK Transport System and How It Compares With the USA - WanderWisdom
London Underground: The UK cities with an underground Tube system you might not know about - MyLondon
How many cities have underground in UK? - Quora
Subway systems by the numbers - BBC Travel
World's oldest metro systems - Railway Technology
List of metro systems - Wikipedia
Bristol could get underground railway to beat road congestion
A tale of two metros: how the London tube beat the New York subway | Underground cities | The Guardian
Revealed: London's secret underground railway system - CNN Style
London Underground: The UK cities with an underground Tube system you might not know about - MyLondon
London Underground: The UK cities with an underground Tube system you might not know about - MyLondon
Why do so few cities in the UK have metro systems? - Quora
End London-centric approach and invest £140bn in 11 underground systems, Scape say | Infrastructure Intelligence
UK Cities with an Underground Metro Service | Binge Travelling
Why do so few cities in the UK have metro systems? - Quora
Britain's Other Underground Train, Tube, Metro Rail Systems, and Networks - Anglotopia.net
MTR - Wikipedia
London Underground | subway, London, England, United Kingdom | Britannica
The last metro? Crossrail and the uncertain future of urban transit | Financial Times
The World's Oldest Metro Systems - WorldAtlas
Which UK cities outside London have subway/metro/underground/tube systems? - Quora
This is why Reading and four other Berkshire towns are on the London tube map - Berkshire Live
London Underground: The UK cities with an underground Tube system you might not know about - MyLondon
