The Jubilee Line Extension has been plagued with difficulties. Praise be, then, for Foster and Partners' inspiring, light-filled station.
Roland Paoletti, London underground's Italian architect in charge of the Jubilee Line Extension, is not afflicted by the English weakness of false modesty. Standing in the concourse of the new Canary Wharf underground station, designed by Foster and Partners and due to open in late summer, he says: "I hope this will do for London Underground what Sydney Opera House did for Australia."

The evidence to support Paoletti's boast is all around him. Although the concourse is fully below ground, we are standing in a vast, cathedral-like hall. And, despite the lack of windows, daylight floods into the concourse from two large, fully glazed entrance canopies in the roof.

There is nothing here to remind one of the traditional underground station – tight, cramped, artificially lit and little more than an extension of the train tunnels. Instead, the scale, daylight and curvilinear forms of the roof slab give Canary Wharf the ambience of a great railway terminus or airport terminal.

Aeronautical imagery, the hallmark of Foster and Partners, is evident in the roof slab and its supporting columns. The fairface concrete columns that form the central row are elliptical or streamlined, while the roof slab, also in fairface concrete, sweeps up and outwards on either side of the columns like a pair of wings. Flying forms may not be an obvious choice to symbolise underground transport, but they give the station a certain grace, lightness and sense of elation.

Other than a few standard components, such as escalators, lighting fixtures, signage and sliding glass safety screens at the platform edges, Canary Wharf bears little relation to the 10 other new and extended stations on the JLE. This is partly because of Paoletti's decision to commission the design for each station from a different architect, as each presented markedly different design problems above and below ground. And, more basically, Canary Wharf is much larger than any other London Underground station.

The reason for such a huge hall is that Foster's station will serve the mini-Manhattan of Canary Wharf and Heron Quays, where clusters of office skyscrapers are bidding to rival the City of London over the next three decades. Passenger throughput at Canary Wharf is expected to rise early next century to a peak of 40 000 an hour during rush hours, making it the second busiest station on the London Underground.

The station has been created out of West India Dock, or, more precisely, the strip of water between Canary Wharf and Heron Quays. The depth of the station was determined by the level of the underground lines passing below the River Thames. Its length was dictated by platforms 210 m long to cater for the JLE's unusually long trains. A "crossover box", or chamber where trains can cross from one line to another, has been added to the length of the platforms. The resulting enclosing structure for the station is an immense, elongated concrete box 280 m long, 32 m wide and 24 m deep. This is equivalent to the neighbouring Canary Wharf tower – Britain's tallest building – laid on its side. The box was created by sinking cofferdams into the dock to form a massive pit inside which the station was built.

The dimensions of the crossover box have been exploited by extending the concourse and the fire-escape stairs directly above it. Extra width has been added to the concourse by allowing it to stretch sideways over the flank walls of the lower platform box.

Externally, the two glazed entrance canopies covering the escalators to the concourse, plus a smaller one located to one side, are all that is visible of the huge engineering structure. The canopies are characteristic Foster – shallow elliptical domes or "bubbles" in frameless glazing, each spanning 20 m and surrounded by projecting guard rails in stainless steel. The canopies appear like gentle glass hillocks within a newly created public park, complete with copses of mature trees, that forms a green lid to the underground station and a link between the two adjoining wharfs.

Inside the concourse, the elongated hall is notable for its clarity and lack of clutter. Other than the waist-height ticket barriers, the central rows of columns and the banks of escalators at either end, the hall is bare. Ticket offices, automatic ticket dispensers, passenger information and building services are all neatly lined up along the two flank walls.

The hall is dominated by daylight flooding through the entrance canopies and down the escalators. "You don't need signage – you just move towards the light to find your way out," explains Foster and Partners' director David Nelson. Even during rush hour, the passenger route through the station could hardly be clearer, and the height should impart a sense of calm to the mêlée below.

The platform level is a similar oblong hall, although slightly narrower and interrupted by the glazed platform screens and five banks of escalators. Even here, 24 m below ground, daylight and even the occasional shaft of sunlight percolate down from the concourse, providing the same natural signage for the way out.

A limited range of materials and monochrome colours enhance the sense of clarity. Exposed reinforced concrete predominates in the concourse, and surfaces within reach of passengers are lined with panels of polished stainless steel and toughened glass.

"We have aimed to give Tube travellers a smooth progression from street level down to ticket hall, then down again to trains, for which signs are barely necessary," explains Nelson. This has been achieved by rigorously rationalising and simplifying an immensely complex building, beset by strict yet sometimes conflicting codes of safety and construction, and by last-minute attempts to save on materials as the entire JLE project escalated in price. However, there is little sign of cheap, last-minute ducting, cabling and safety gear being tacked on to finished surfaces of the building as a result of cost-cutting.

Seemingly hard-and-fast safety regulations have also been judiciously bent, although with the interests of passengers in mind. Artificial lighting levels in the concourse have been kept below the regulation standards, as the architect convinced the engineer that perceived lighting was more important than actual lighting. The effect is to reinforce the daylight streaming through the glazed entrance canopies. As well as enhancing the architectural beauty of the building, the daylight literally highlights the exit routes.

Paoletti is clearly delighted that the station has survived the pressures of Europe's largest civil engineering project and that it closely matches the initial design exhibited at the Architectural Foundation seven years ago. The building also fulfils his vision for the JLE stations by allowing the underlying civil engineering structure to express itself openly in the finished architecture.

Of course, Sydney Opera Houses do not come cheap, and Paoletti admits that extra expenditure was channelled into Canary Wharf Station. "We said at the beginning that we would make one or two stations more elaborate where this was justified by higher population densities. We have put a lot of eggs into that basket at Canary Wharf, but I hope it will give a feeling of optimism to the Tube in London."

Paoletti has a more poetic metaphor to explain the widely differing treatment and expenditure on the 11 JLE stations, which has puzzled onlookers. "The JLE is like a tune, like jazz," he says. "The whole piece has movement and integrity. But within the tune, there are crescendos. Canary Wharf is one of these crescendos."

How engineering became architecture

A limited but carefully considered palette of materials has been used to enhance the visual clarity of Canary Wharf Station and to provide hard-wearing, safe and easily maintained finishes within a tight budget.
  • Reinforced concrete The dominant material is the insitu reinforced concrete of the structural columns and floor slabs, which has been left as a smooth, fairfaced finish. “The engineering manifests itself as the architecture,” says Foster and Partners director David Nelson. “It’s very intentionally raw concrete, though we worked with a concrete adviser, Bill Monks, to get the aggregate and mix right. The marks and blemishes give it a handmade finish that distinguishes it from the other materials, which are all prefabricated.”
  • Stainless steel and glazed panels All surfaces within reach of passengers are lined in panels of polished stainless steel or toughened glas (clear or sand-blasted, supplied by Issiglass) that are resistant to vandalism and wear and tear. The smooth panelling has been detailed with flush profiles and joints that can be washed down without leaving streaks.
  • Reconstituted stone flooring The flooring is composed of reconstituted stone slabs that are tougher than terrazzo but cheaper than granite. The slabs were cast by Maling Pre-cast with a rough, slip-resistant finish impregnated with a silicone-based sealant.
  • Profiled metal wall linings Above the reach of passengers, the internal walls and services ducts are lined in standard profiled metal sheeting in charcoal grey, supplied by Harty Holdings. This was a cheaper option than the extruded aluminium louvres in the original design.
  • Sound absorption to walls and ceilings Sound-absorbing Rockwool quilting applied to the upper surfaces of the walls is encased within expanded metal lath, which has been painted charcoal grey and looks remarkably sophisticated. Sound absorbers applied to the concrete ceilings, supplied by HT Martingale, take the form of a series of metal tubes carefully positioned to break up sound waves, and are backed by fibrous acoustic boarding. The series of white-painted tubes also adds texture to the concrete roof slab.
  • Frameless glazing to entrance canopies The double-curved, bubble-shaped canopies are composed of frameless glazing using single-curved laminated glass panels, as it proved too difficult to curve each panel in both directions. However, as many as 96 different shapes and sizes of glass were needed for each canopy, and were supplied by Mero.