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A woman sleeps in front of a painting decorating a subway station in Buenos Aires, Argentina, Wednesday, Sept. 17, 2014.

Natacha Pisarenko/AP

A woman sleeps in front of a painting decorating a subway station in Buenos Aires, Argentina

Commuters board an underground train at King's Cross station in London April 29, 2014. Millions of commuters faced transport chaos on Tuesday after eleventh-hour talks failed to avert a two-day strike on the London Underground train network over plans to cut jobs and close ticket offices.

Neil Hall/Reuters

Commuters board an underground train at King’s Cross station in London. Millions of people faced transport chaos on Tuesday after talks failed to avert a two-day strike on the London Underground train network over plans to cut jobs and close ticket offices.

Commuters take a bus in central London, ...Commuters take a bus in central London, on February 5, 2014, on the first day of a strike by London Underground workers. Workers on London's Underground train system kicked off a 48-hour strike at 9:00 pm (2100 GMT) on Tuesday, threatening chaos for commuters on Wednesday and Thursday.   AFP PHOTO / BEN STANSALLBEN STANSALL/AFP/Getty Images

Ben Stansall/AFP

Commuters take a bus in central London, on the first day of a strike by London Underground workers. Workers on London’s Underground train system kicked off a 48-hour strike at 9pm on Tuesday. 

ames Apps, six, looks at the 2020 Tube map of the future, made entirely from LEGO Bricks, at LondonĂ­s King's Cross Station to celebrate 150 years of the London Underground.

Geoff Caddick/PA

A child examines the 2020 Tube map of the future, made entirely from Lego bricks, on display at London’s Kings Cross Station to celebrate 150 years of the London Underground.