Swiss police officers stand beside of mock gates of the NEAT Gotthard Base Tunnel inside the event hall for the upcoming opening ceremony near the town of Erstfeld, Switzerland May 31, 2016. The celebrations of the opening of the Gotthard Base Tunnel will start on June 1, 2016. With a length of 57 km (35 miles) crossing the Alps, the Gotthard Base tunnel is the world's longest train tunnel. (Photo by Arnd Wiegmann/Reuters)

An Afghan National Army (ANA) helicopter flies over a soldier during a training exercise at the Kabul Military Training Centre in Afghanistan October 7, 2015. (Photo by Ahmad Masood/Reuters)

Migrants with a stick, stones and knife fight with each other after a brawl erupted over a place in an overcrowded train heading to the Serbian border at the train station in Gevgelija, The Former Yugoslav Republic of Macedonia, 14 August 2015. The number of migrants passing through Macedonia increases day by day, local sources said. From the beginning of the year to mid-June 2015, nearly 160,000 migrants landed in the southern European countries, mainly Greece and Italy, on their way to wealthier countries in Western and Northern Europe, according to estimates by the International Organization for Migration (IOM). (Photo by Georgi Licovski/EPA)

Soldiers of China's People's Liberation Army march with their weapons during a training session for a military parade to mark the 70th anniversary of the end of World War Two, at a military base in Beijing, China, August 22, 2015. Troops from at least 10 countries including Russia and Kazakhstan will join an unprecedented military parade in Beijing next month to commemorate China's victory over Japan during World War Two, Chinese officials said. The parade on September 3 will involve about 12,000 Chinese troops and 200 aircraft, Qi Rui, deputy director of the government office organizing the parade, told reporters in Beijing on Friday. (Photo by Damir Sagolj/Reuters)

A girl looks out from the window of a “La Sabana” tourist train in La Caro March 1, 2015. The “La Sabana” tourist train that runs through the capital was founded by Eduardo Rodriguez, a railway engineer. Rodriguez has worked on Colombia's railway system his whole life and now, with an air of nostalgia, transports thousands of tourists in renovated steam locomotives that he fixes in Bogota's Central Station which dates back to 1913. (Photo by Jose Miguel Gomez/Reuters)

Jordanian policewomen train in unarmed combat in the training city August 21, 2008 in Muwaqqar, east of Amman, Jordan. A women's police academy opened in Amman in 1972 making Jordan the first Arab country to admit women to its police services. Jordanian policewomen work as personalities' guards, special security operations and traffic policewomen including motorcycling among other professions. (Photo by Salah Malkawi/Getty Images)

A man stands on an old train of Bolivian Railways Company from 1870-1900 at the train cemetery in Uyuni, Potosi, Bolivia on May 16, 2018. (Photo by David Mercado/Reuters)

Bangladeshi Muslims travel on the roof of an overcrowded train as they head to their hometowns ahead of Eid al-Adha in Dhaka, Bangladesh, Friday, September 1, 2017. The festival commemorates the story of Abraham and his readiness to sacrifice his son as an act of obedience to God, who provided a lamb to be used instead. (Photo by Bernat Armangue/AP Photo)