Hong Kong – Passengers on a Mass Transit Rail (MTR) train in Hong Kong.
Hong Kong – The MTR is renowned for being immaculately clean, well-signposted, cheap, and punctual. There's free Wi-Fi in every station in Hong Kong, facilities such as tactile flooring and Braille plates for travelers with disabilities and public washrooms, shops, banks and takeaway food outlets inside many stations or close to their exits.
London, England – The London Underground, also known as "The Tube," is more than 150 years old -- making it the oldest metro in the world.
London, England – The London Tube was the world's first underground metro, opening in 1863. Since then, air-conditioned carriages have been introduced, alongside intermittent Wi-Fi signal. The Underground services more than 1 billion journeys per year.
Tokyo, Japan – The rail and subway network within the Japanese capital is a vast system with 17 lines in total -- 13 of which make up the city's subway.
Tokyo, Japan – A poster informing commuters of a women's-only carriage is displayed on a subway train in Tokyo on June 2, 2017.
New York, United States – New York City's MTA subway lines are doubled up so all local and express trains can run simultaneously along the same routes, 24 hours a day. Even when carrying out major work on a line, only a single track is decommissioned, leaving a reduced but still-open service.
New York, United States – Passengers on the New York City subway.
Paris, France – The French capital has some of the most distinctive Metro branding in the world.
Paris, France – With more than 1.5 billion passengers a year, Paris Metro is one of the top-five busiest city-rail services in the world.
Moscow, Russia – The ornate interior of Komsomolskaya Metro Station on the Koltsevaya Line of the Moscow subway. The station was opened in 1952.
Moscow, Russia – Subway passengers walk through Mayakovskaya station in Moscow.
Beijing, China – Commuters wait to enter a subway station during the morning rush hour in Beijing. Despite some five million private vehicles in Beijing, public transport faces heavy congestion on a daily basis as most of the city's 21.5 million people head to work.