Advance warning on the blue distraction

The giant blue gantry is helping replace the Newmarket Viaduct in sections at a cost of $215 million. Photo / Dean Purcell

Transport Agency contractors intend using YouTube to reduce the chance of drivers being distracted by the $215 million Newmarket Viaduct construction project and its eyecatching huge blue gantry.

As the first of eight sections of what will soon become a 110m gantry are lifted into place, they are preparing to post a 3D animation on the video-sharing website next week to outline how the viaduct is being replaced between now and 2012.

That is in addition to traditional newspaper and radio advertising, and will be aimed at reducing the element of surprise for the 160,000 motorists who travel daily across the viaduct and may become distracted by an overhead structure too large to be hidden from their gaze.

The 700-tonne gantry, which was also used to build a bridge over the Waiwera River for the Northern Gateway toll road, is being erected on top of 44 sections of a new southbound viaduct that have already been constructed.

It will be ready by early January to "launch" remaining 70-tonne to 84-tonne sections of the 690m viaduct, off supporting piers up to 18m high.

But engineers consider that to be a relatively straightforward task compared with its next mission - of demolishing the existing viaduct to make way for a replacement northbound structure.

For that, the gantry has had extra steel added since being transferred from Waiwera to the heart of Newmarket.

Tonnes of temporary supporting steel will also have to be erected under the existing northbound viaduct to ensure the southbound carriageway can be demolished without toppling it.

Work on this stage is expected to start next September.

Although a 70km/h speed restriction has been in place on the viaduct's southbound lanes since August, project officials say that measure has become even more critical now that the launching gantry is growing in height and size.

They are not so worried about daytime traffic, which is usually too heavy to move fast, but want to ensure night drivers do not hit the viaduct at high speeds at which a moment's distraction could prove fatal.