Mott MacDonald pulled off an incredible engineering feat in Boston that involved creating the world's largest man-made iceberg – making it a clear winner in this category
1st - Mott MacDonald
Boston's Central Artery project had the simple aim of taking a significant part of the city's traffic underground. All that was required was a tunnel 10 times larger than any jacked tunnel ever built in the USA before, and one of the world's best engineers to make it work at a price that the authorities could afford. Enter Mott MacDonald. Its team found a way to route the equivalent of three motorways under a continuously operating railway using structural elements weighing up to 30,000 tonnes – a feat requiring the largest ever ground-freezing operation. The pay-off for Boston is that the whole downtown area can communicate with itself again, free of the semi-permanent traffic jam on the old elevated highway. What's more, British engineering in general, and Mott MacDonald in particular, have confirmed their reputations as world leaders.

'Its impressive Boston road tunnel is an engineering tour de force and has won lots of praise from transportation commentators in the USA'

2nd - FaberMaunsell
This consulting engineer set a performance benchmark in its work on the M&E services for the extension of the National Gallery of Ireland. FaberMaunsell met all of the stringent temperature control and relative humidity requirements with aplomb. Other triumphs last year included its success in the international competition for the Athletes' Village at the Turin Winter Olympics, and the integral part it played in the ambitious Copenhagen metro scheme.

'A string of international projects, from the award winning National Gallery of Ireland to the 2006 Winter Olympics village in Turin'

3rd - WSP International
Last year WSP added to New York's skyline the $400m Trump World Tower, which, at 70 storeys, is the highest residential building in the world. The engineer overcame a number of problems caused by the slenderness of the building relative to its height, and pioneered the use of 12,000 psi concrete in New York. The success of the project has turned WSP, through its Cantor Seinuk subsidiary, into a leading performer in the US tall building sector.

'Its recently completed Trump World Tower is the tallest residential building in the world'

4th - Benoy
Architect Benoy used its designs for the Bluewater retail centre in Kent – the largest in the country – to break out of the increasingly tough UK market. More than 450 clients were taken on tours of Bluewater, and as a result the practice's overseas work is now about 45% (from zero in 1999), and it includes retail schemes worth £180m in Spain, £100m in Hong Kong, £130m in Greece and £120m in Saudia Arabia. Not bad from a standing start.

5th - Dewhurst McFarlane and Partners
The jewel in the crown of this consulting engineer was Rafael Vinoly's $260m performing arts building in Philadelphia, known as the Kimmel Centre. The firm devised a dynamic weight system that was a breakthrough in the engineering of glass cable wall systems – and a huge risk for the engineer, which took on the liability for its system working. The success of Kimmel led to two other commissions in the USA, both with cable-supported end walls.