One key section of the massive Terminal 5 project at London's Heathrow Airport works to different rules.
Dave Parker reports from the station box.
For many, the first experience of BAA's flagship Terminal 5 will come when their train stops at the station underneath the terminal. People could alight from a London Underground Piccadilly Line train or the Heathrow Express - in years to come they may have travelled direct to Heathrow on heavy rail from far to the west. However they arrive, BAA is determined that its customers have as smooth a transition from station platform to the departure lounge as possible, both physically and psychologically.
'This means using the same finishes and fittings in both terminal and station - as far as possible, ' explains head of T5 rail and tunnels Ian Fugeman.
'But the station has to be designed to comply with railway rather than building safety and environmental regulations, which means generally tougher specification for fire resistance and spread of flame, more robust CCTV and so on.'
Another key difference is the internal environment, which will be much more aggressive than in the terminal above, thanks mainly to carbon dust from Heathrow Express train brakes. There will be no conventional air conditioning; air will be changed largely through the pumping action generated by the trains themselves.
Heat from the trains' running gear can be drawn off via ducts below the platforms.
BAA has invested heavily in the station, Fugeman points out, spending far more than required by the planners. 'If you are going to do it, do it properly, is our philosophy, ' he adds. The result is a rail terminal on the grand T5 scale, with room for future expansion built in, all contained within a concrete box some 250m long by 90m wide by 6m high.
Ranged across the box will be two platforms with space alongside for a future platform to handle heavy rail. Each is wide enough (up to 25m) to have a spacious central concourse. The northern platform is earmarked for Piccadilly Line trains, the central one for the Heathrow Express.
Until plans for heavy rail connections to the west become reality, the southern platforms will not be built, and a concrete wall will hide the blank space.
Walls, albeit with frequent windows, will back each platform - for smoke control and draught management, explains T5 station delivery manager Keith Heard. 'But the station won't feel constrained, ' he adds.
'From key passenger concentration points on the platforms and concourses it will be possible to see right across the station in both directions through the windows in the walls.'
Linking the precast concrete platforms in the box and the departures floor more than 30m above will be 'T5's biggest lifts': five 55 person glass fronted cars per platform.
Once they quit the lifts passengers will walk across an 18m span bridge and through a 'letterbox' in the dramatic glass cladding of T5A, the main terminal building.
At some invisible point on this last step of their journey they will pass from the territory of Her Majesty's Inspector of Railways and into an environment governed by the local planning authority - but BAA's design team is doing its best to make sure no one can tell the difference.
One difference is hard to disguise, as Herd explains.
'The steel framed lift towers are very stiff, and will move laterally by no more than 25mm.
'But T5A is so large it can sway up to 150mm. We had to come up with a very special synthetic rubber gasket design to cope with the differential movement.'
On their way up, departuresbound passengers will be treated to an unrivalled view of the dramatic 90m by 30m ETFE roof over the apron level Interchange Plaza - in fact they will pass right through it.
This roof protects arrivals passengers heading towards the massive multi-storey car park from the 'onward travel centre'.
Only two of the three planned lift towers will be built at first: the third will serve the future heavy rail platforms. Whichever lift a T5 user chooses, the ride promises to be very special.
Station architect: HOK
Civil & structural engineer: Mott MacDonald
Stations and tunnels fit out contractor: Balfour Beatty
Cut and cover box contractor: Laing O'Rourke
Tunnel contractor: Morgan Vinci JV
Heathrow Airport's network of underground rail tunnels is nearing completion. The existing Heathrow Express and Piccadilly Line loops that currently serve Terminals 1, 2, 3 and 4 have to be significantly extended to serve T5, a procedure that inevitably involves new tunnels crossing the line of existing tunnels.
Some disruption to rail services is inevitable - the Piccadilly Line link to Terminal 4 will close for 20 months to allow the complex junction between the old and new lines to be constructed (NCE Terminal 5 special February). Connecting to the Heathrow Express (HEX) is much more straightforward, as Fugeman explains.
'When the Piccadilly Line was extended to Terminal 4 it was assumed that any future terminals would be quite close to Terminals 1,2 and 3. So a straight was constructed just to the east of where T5's maximum eastward extension would be.
'However, by the time the Heathrow Express was built in the 1990s, BAA had a pretty good idea of T5's actual location. So it incorporated a stub end in the up line, and, during construction, decided to build a head shunt at the crossover where the two HEX lines converge into one.'
However, neither the four rail tunnels nor the various other baggage, road and stormwater outfall tunnels on the T5 site could be allowed to disrupt air operations. Potentially the most risky moments are when new tunnels pass under existing lines. So far, says Fugeman, with 12km of the 13.5km of tunnels complete - not including the cut and cover sections - 'everything has gone very well, without any impact on airport activities'.
Work has just started on the last T5 tunnel, the HEX extension up line, which will also have to pass under the Piccadilly line.
When construction began, two rivers - the Twin Rivers - still ran between what is now T5A and its satellite, T5B. Cut and cover construction was used for the tunnels either side of the rivers. Now the rivers have been safely diverted away to the west, the way is clear for a linking section to be inserted.
The station box, massive as it may be, is not the end of the line. Another cut and cover box runs out to the west, stopping just short of the site boundary.
Its only operational use in the near future is to house an essential Piccadilly Line reversing siding. Its existence, however, is another example of BAA's positive thinking. Should anyone in the future wish to link in heavy rail from the west or extend the Heathrow Express even further, then a ready-made connection will be ready and waiting.