Next to the World Trade Centre site, Arup and Grimshaw have designed one of Manhattan's most dramatic projects. It may not alter the skyline, but the £500m subway interchange will transform the city's congested and confusing underground network.

While Crossrail and other ambitious additions to London's creaking transport network are little more than items on Ken Livingstone's wishlist, his counterparts over the pond are getting on with it big time. Not only is the construction of a new subway line running the entire length of Manhattan due to start later this year (see 'A long wait for a train', page 44), but plans were unveiled at the end of May for a £500m transport interchange a few blocks away in downtown Manhattan.

Located alongside the World Trade Centre site, the Fulton Street transit centre is due for completion by the end of 2007 and is one of New York’s most ambitious public sector redevelopments to be undertaken since the 9/11 catastrophe in 2001. The project team is led by British engineer Arup, with Grimshaw as architect for the station entrance building and 110 m underground concourse. According to Bill Wheeler, the director of planning for Metropolitan Transportation Authority, “Arup and Grimshaw were selected because they brought a unique creativity to the process.”

Grimshaw's Fulton Street entrance building will be the centrepiece of the interchange – above ground at least. It will take the form of a gleaming glass box with a glass cone erupting out of it. The rounded form and diagonal grid perimeter structure of the cone bear a passing resemblance to Foster and Partners' Swiss Re tower in London, though its lop-sided shape and flat top suggest a glass volcano rather than a gherkin.

Inside, the glass volcano turns out to be a vast hollow dome encircled by shops and cafes at the entrance and the mezzanine levels. The flat top is a large glass lens, which will shine sunlight down two floors below pavement level into a round circulation area at one end of the new underground concourse.

The glass building will replace an old mid-rise office block that had a dingy subway entrance at pavement level. In the same way, the whole interchange project represents a dramatic upgrade of existing facilities. Although no new subway lines are to be added, passenger access to 12 existing lines will be improved.

The problem is that, back in the early 20th century, the 12 subway lines and six stations had been separately developed over an area of four city blocks by competing private companies. Although it has since been amalgamated by the Metropolitan Transportation Authority, the network still presents the 275,000 passengers passing through every day with a labyrinth that is congested, confusing, circuitous, gloomy and an obstacle course for disabled people. By replacing the jumble with one streamlined interchange, the project is intended to make access clearer, more spacious and disabled-friendly. And with 85% of all downtown access trips made by public transit, it is little surprise that the MTA website declares that lower Manhattan “urgently needs a clear connected subway complex and gateway to support its economic revival”.

Grimshaw's glazed entrance building and the concourse below it, which runs the length of three city blocks and connects six subway lines, provide the intended gateway and much of the clear connection. Other improvements to the complex will include refurbished and expanded stations, new underground passageways between stations, new lifts and escalators and new street entrances.

Although the project has been in planning for a number of years, the 9/11 disaster has given it fresh impetus. Arup was awarded the design contract last August and completed the concept design in less than two months. The plan is to let the first construction projects by the end of this year, with completion three years after that.

Wheeler says the biggest challenge will be to carry out construction without disrupting passengers and through trains, which in New York carry on continually 24 hours a day, seven days a week. “Pathways are left open for passengers, and lots of men with flags slow down trains as they pass through the works,” he says.

The importance of the interchange project is explained by David Palmer, Arup's project director: “It will play a major part in making downtown one of the most accessible business districts in the world, and one of the best places to work, visit and live in New York city.” This optimism is not without grounds, particularly as, at street level, the subway improvements link up with the pedestrianisation of downtown east of Broadway, as directed by New York’s mayor, Michael Bloomberg.

All of which is probably enough to make Ken stare wistfully at his wishlist and long for some of that Broadway magic.

A long wait for the train: New York’s new subway line

New York’s other big infrastructure project is to insert a subway line the whole length of Manhattan beneath Second Avenue. The line will cover 8.5 miles and will include 16 new stations plus an interchange at 125th Street. Arup has been appointed as one of three prime consultants.

What seems like an extravagant addition to New York’s comprehensive subway network turns out in fact to be more of a replacement for two long-demolished lines. Two “Els”, or elevated railways, ran along Second and Third Avenues in the early 20th century but were demolished in the 1940s and 1950s, leaving the eastern flank of Manhattan bereft of rapid transit. Plans to replace the Els with a subway line stretch back to 1929, and construction even started in the late 1960s before being brought to a halt by the city’s financial crisis in the 1970s.

The current plans were started by the Metropolitan Transportation Authority in 2001. Construction using design-and-build contracts is planned to start at the end of this year for completion in 2011.

The plan is to construct the subway in four phases without closing streets. To cut through the Manhattan rock, three different forms of underground construction will be adopted. Much of the tunnel will be bored using a powerful circular cutting machine. Being wider and deeper, the stations will be excavated by cut-and-cover techniques, above which a temporary metal deck will be laid so that the street can remain open to traffic. In short or curving sections of the tunnel, mining methods of drilling and blasting will be used. Much of the spoil will be removed by barge.

Project Team

client Metropolitan Transportation Authority

prime consultants Vollmer Associates (environmental impact), Arup (engineering), DMJM + Harris (engineering)