A £13.3bn tunnel is being built beneath one of the world’s biggest cities. The Second Avenue Subway is a New York tunnel running under the east side of Manhattan.

The proposed full line would run for 8.5 miles and have 16 stations – and it could serve up to 560,000 daily riders. It was built partly to relieve pressure on the busy Lexington Avenue line, the only north-south subway on the east of the city.

Phase one of the project was completed in 2017 with the opening of three new stations on the city’s Upper East Side from 72nd Street to 96th Street. 

Phase two is currently underway. It will extend the Q line into Harlem to improve transportation. It will connect Harlem to Lower Manhattan.

Phases three and four, which both have no funding commitments, would connect 63rd Street to Hanover Square through Houston Street.

The line was originally proposed in 1920 as part of a massive expansion of the subway system. After many false starts over the last 100 years, work finally began in 2007. The proposal went to a public vote and it only passed with a 10 percent margin, with 55 percent of voters in favour.

The first phase cost £3.46bn, with the total cost of the project set to soar above £13.3bn.

The Second Avenue Subway’s per-mile construction cost is higher than that of other projects in similar cities like London’s Crossrail and Paris’s Grand Paris Express, which themselves are among the most expensive underground-railway projects in the world. 

MTA officials stated that the Second Avenue Subway cost as much as it did because of the complex underground infrastructure in Manhattan, as well as the fact that the New York City Subway operates 24/7 service.