Today, the Underground carries more than 1 billion passengers a year on 11 lines serving 270 stations, ranging from the cavernous and modern Westminster to red-bricked Edwardian-era relics like Belsize Park.
But there have been undeniable growing pains. Most of the Underground's construction occurred between the mid-19th century and 1930, and a system that old is very expensive to maintain and expand, says Tony Travers, a local government expert at the London School of Economics, where he heads the university's London research center.
The Underground is not alone in coping with the challenges of old age. Boston's "T," the oldest subway system in the United States, began operations in 1897, with the Paris Metro (1900) and New York City subway (1904) following right on its heels. All have struggled to keep pace with urban sprawl and population expansion not planned for when they were constructed more than a century ago.
London responded to increased strain on its system with two new lines in the 1960s and '70s – Victoria and Jubilee. And Europe’s largest civil engineering project, a major rail line connecting east and west London and known as Cross Rail, is currently under way.