this week marks the 111th anniversary of the opening of new york city’s subway, the big apple’s famous underground rail system. opening on oct. 27, 1904, it cost a nickel for a ride and more than 100,000 commuters took their first subway trip that night. though boston and london both had running subterranean trains by 1897, the subway in new york grew to become the largest in us.

today the subway serves 4.5 million people daily and has a 24-hour operating schedule, making it the only rapid transit system in the world that always runs in its entirety — fitting for the city that never sleeps. even as the largest underground transit system in the u.s., there are still proposals and works in progress to expand the reach of the subway to make it more convenient for commuters.

unfortunately, the outlook is not bright for underground trains in coastal cities — especially in the big apple, which is far enough below sea level that it is already threatened whenever a tropical storm happens to travel north. as global warming causes an increase in sea level, the city will face a higher threat of flooding each year. even as recently as 2012, the subway system was devastated by hurricane sandy resulting in $5 billion worth of damage.

if the sea level should rise by a meter or more over the next century, new york city may find itself underwater with a waterlogged and salt corroded transit system after every storm. of course, this is a problem for every coastal city as the u.s. falls behind in innovations to combat rising sea levels. hopefully, progress will catch up with the problem and the many subway-dependent commuters will still have their trains for many years to come.

(image at top: the city hall subway station in the early 1900s. source: library of congress)