subway

A woman walks past Greenpeace environmental activists dressed up as a polar bear in Prague October 13, 2014. The event is part of a campaign to raise awareness about the threats to the Arctic and to advocate a ban on drilling for oil.

David W Cerny/Reuters

A woman walks past Greenpeace environmental activists dressed up as a polar bear in Prague. The event is part of a campaign to raise awareness about the threats to the Arctic and to advocate a ban on drilling for oil

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 walk under the rain along Comercio square during a partial strike by Lisbon's subway workers, in Lisbon, Wednesday, Sept. 10, 2014. The subway staff walked off the job during the morning rush hour in a protest against pay cuts and the company's possible privatization. The strike brought misery to commuters who faced long queues for buses in the rain.

Francisco Seco/AP

Commuters walk in the rain through Comercio square during a partial strike by Lisbon‘s subway workers on Wednesday

Chinese commuters line-up for a security check at a subway station on May 29, 2014 in Beijing, China. Authorities have increased security in various public locations after an attack left 31 dead in the restive Xinjiang Province last week.

Kevin Frayer/Getty Images

Chinese commuters line up for a security check at a subway station on Thursday in Beijing. Authorities in China have increased security in public locations after an attack left 31 dead in the restive Xinjiang province last week

China Daily Life - Construction...BEIJING, CHINA - MARCH 29: Chinese workers eat lunch and rest at the site of a new subway line on March 29, 2014 in Beijing, China. The new line will be the 18th in the Beijing subway system, which has a daily ridership of more than 10 million people, according to local officials.

Kevin Frayer/Getty Images

Chinese workers break for lunch at the site of a new subway line in Beijing, China. The line will be the 18th in the Beijing subway system, which is used by more than 10m people a day, according to local officials.

A man takes part in the annual No Pants Subway Ride in New York

Eric Thayer/Reuters

A passenger takes part in the annual No Pants Subway Ride in New York on Sunday. The event started in 2002 in New York and has spread to 60 cities in 25 countries.

Mona, an Iranian girl, sells fortune papers in a subway in Tehran, Iran, 07 January 2014. International sanctions against Iran in connection with the country's controversial nuclear programmes have led the country into an economic crisis, forcing even children helping out their families as street vendors.

Abedin Taherkenareh/EPA

Mona sells fortune papers in a subway in Tehran, Iran. The country’s economic crisis has forced many children into work to help their families

Contractors work on the East Side Access project beneath Grand Central Terminal, Thursday, April 18, 2013 in New York.  When complete the East Side Access project will connect Long Island Railroad trains to Grand Central Terminal serving approximately 160,000 customers a day. It is one of three bold projects under New York that will expand what's already the nation's biggest mass-transit system by 2019.

Mary Altaffer/AP

Contractors on the East Side Access project beneath Grand Central Terminal in New York on Thursday. When complete the project will connect Long Island Rail Road trains to the terminal serving about 160,000 customers a day. It is one of three bold projects under New York that will expand what’s already the nation’s biggest mass-transit system by 2019.