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The airport operator has therefore created an optimal IT system: this means that the whole project team works within one common 3D computer model. This will be used to design, build and maintain T5 with the objective of cutting 10% from the project cost. "It's all about trying to get people to collaborate and communicate with each other rather than working in isolation then throwing the information over the wall," says Andrew Manington, BAA's production support manager. "This produces better quality information, reduces ambiguity and clashes and gives more certainty on time and cost earlier in the project."

BAA's post mortems on its previous projects have shown that they went over budget because of inconsistencies in drawings. Conventionally, the architect designs the building and passes the CAD drawings to the engineer. The engineer then draws the building again using a different program to do the engineering analysis 鈥� in itself a process that is guaranteed to introduce errors. This procedure cascades down the team to the specialists and their design departments, until hundreds of sets of drawings of the same structure have been created. The inevitable inconsistencies between these drawings have to be reconciled on site, leading to problems with delay, workmanship and cost. So, "the idea behind the single-project model is to derive an unambiguous set of data through the sharing of data", says Mervyn Richards, Laing O'Rourke's CAD technology manager. "With this, the engineer never redraws the information; it can reuse the architect's data and add to it. We are getting everyone to work on the same data set to drive out error and improve efficiency."

The massive roof nodes that connect the roof structure together are good example of how the single-model environment works. Richard Rogers Partnership designed the node and passed it over to Arup, which was acting as structural engineer. Arup used the architect's drawing to carry out the structural analysis before returning it RRP for design modifications. After that was done, the model was passed to steel fabricator Severfield-Rowen, which used it to fine-tune those parts of the node that had to be specially made. Finally, they used the model to control the computer-aided manufacturing machinery that shaped the roof parts.

Information contained in the model has been used during the construction phase. It has supplied information to plan the methodology for constructing the building, and for managing time efficiently. It has also contributed to better health and safety because it has eliminated the need to botch together impromptu solutions to the drawing errors. The model is constantly updated with as-built information in case of small variations on site. Now that the concrete and steel structural work is finished, the fit-out contractors can use this information to do the detail design on their part of the project, including the complex baggage-handling systems. "This gives us tremendous confidence that the baggage-handling systems will fit," says Manington.

The model will also help the airport operator make savings in maintaining its buildings, and will increase the team's knowledge base for future projects. "We need to tie the model into the facilities management systems 鈥� so if, for example, you find a series of valves that keep failing you can change the specification on the next project," says Manington. "You can forget that you need to keep replacing that valve because maintenance teams change so often." The FM teams and others without specialised CAD skills or software will be able to see the information in the model as it can be accessed on BAA servers using a 3D viewer called NavisWorks.

The single-model environment incorporates intelligent object technology to further improve efficiency. This means that objects in the drawing possess information about themselves and how they relate to other objects in the building. "The FM team will be able to go into the model, walk through the corridors, click on objects and retrieve data about that item," says Richards. That information will make it easier to service or replace the component. In the future, manufacturers could make their products available as intelligent objects on the web and designers could download them into the model so it will be easier to keep information accurate.

The drawback to the common data environment 鈥� if drawback it is 鈥� is that discipline is needed to make it work. Everyone who uses it has to follow the same rules. Richards says: "We have had to lay down a series of protocols that say how data is managed and moved around." This includes getting team members to ensure CAD data is dimensionally correct and produced at full size to the same co-ordinates. There are conventions for naming different parts of the drawing and data exchange is carefully managed. Clash detection software is used to check that everyone has stuck to the procedures. If a lapse is discovered, the reason is identified, and if necessary, further training given.

The aspirations for this rationalisation of the construction process are bearing fruit. "So far we have been on target with time and cost as the single-model concept is giving real visibility," says Manington. "What I hope is we will know about the time and cost issues all the way through the project to its completion even though the more complex stuff is yet to come." The rest of the industry will benefit from BAA's work, too. Lessons learned at T5 are being fed into a DTI-funded project called Avanti that aims to show how smaller projects can benefit from the single-model environment.