Public transport in Tallinn has been free since 2013; a political decision taken to help ease the cost-of-living for citizens. Environmental motivations were secondary, but as more and more places seek to decarbonise in this way, the European pioneer has become an unexpected trailblazer.
The Shanghai Metro is the world's longest metro network at 803 kilometres (499 mi) and has the highest annual ridership at 2.83 billion trips. The New York City Subway has the greatest number of stations with 472.
The Sumerian city of Uruk (modern-day Iraq), allegedly home to the legendary king Gilgamesh, topped the list with 40,000 people. It was followed by Memphis (Egypt) with 20,000 inhabitants.