The two largest tunnel boring machines to ever operate in Australia moved a step closer to starting work beneath Brisbane streets following the signing of a $90 million contract today.Deputy Premier and Minister for Infrastructure and Planning Paul Lucas said the signing of the contract between Thiess John Holland and German company Herrenknecht was a major step forward for the massive Airport Link road and tunnel project."When complete, this project will allow motorists to bypass 18 sets of traffic lights between Bowen hills and the Airport, cutting the trip to as little as nine minutes," Mr Lucas said. "Combined with the construction of the next stage of the Northern Busway from Windsor to Kedron and the Airport Drive connection flyover this is the biggest road and tunnel project in Australia's history."

Mr Lucas said each of the tunnel boring machines would chew through around 85m of rock a week.

"These state-of-the art tunnelling wonders will be specially designed and manufactured in Germany for use on Airport Link."

Features of the tunnel boring machines include:

• The biggest ever disc-cutters to operate in Australia at 12.48m in diameter - half the width of an Olympic swimming pool,
• Each disc-cutter features 80, 42.5cm cutters made of hardened steel,
• 165m long and weighing 3000 tonnes - equal to the weight of 75 semi-trailers,
• Able to cut through rock six to eight times harder than concrete while remaining safe to use in softer ground,
• Each machine requires a team of 22 expert operators at all times,
• Both machines will travel 55m below the surface at the deepest section, and
• Each will install a full circle concrete lining continuously as part of the excavation process.

Mr Lucas said both tunnel boring machines would be launched from Toombul and drill Airport Link's east-west connection to Kedron.

He said the final design for Airport Link featured significantly more tunnelling than originally planned, which was good news for motorists and locals alike.

"Using more underground tunnels to build Airport Link reduces the amount of surface works, which means less disruption for local communities and less impact on traffic."

Mr Lucas said the first tunnel boring machine was expected to arrive from Germany by the end of next year and begin tunnelling around mid 2010. The second is expected to arrive in early 2010.

"These are purpose-built from the ground up and while they'll take around a year to manufacture, two months to ship and four months to assemble there'll be plenty of work happening in the meantime.

"Unlike the North-South Bypass Tunnel, Airport Link has connections going east-west as well as north-south. And work on the larger and longer tunnel that runs north-south from Bowen Hills to Toombul will start by the end of this year.

"The good news is that BrisConnections believes it can complete work on all three projects by mid 2012 - six months ahead of the State Government's original plans."