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Strengthening work on the Kawarau River Bridge on State Highway 6 between Cromwell and Queenstown will cause delays for motorists next week.
NZ Transport Agency senior network manager John Jarvis said repairs to expansion joints in the bridge's deck would begin next Monday and continue until the following Saturday.
Traffic would be reduced to a single lane with a 10kmh speed restriction and, although delays for motorists would be ''minimal'', vehicles over a certain weight would be unable to use the bridge throughout the week.
Road transport operators had been advised of the restrictions.
Mr Jarvis said the $1.1 million project, which began in January, would extend the life of the 50-year-old bridge and remove the need for restrictions on ''overweight'' vehicles exceeding 40 tonnes.
The building boom in Queenstown in the past decade had meant more cranes and special loads had needed to use the bridge, but they had been subject to restrictions.
''It's a steel structure and it really isn't designed for the 21st century vehicles that go across it.
''There wasn't anything seriously wrong with the bridge, but it would have become serious if this hadn't been addressed,'' Mr Jarvis said.
When the work was completed, the bridge would be ''like brand new''.
Contractor Fulton Hogan had already replaced 1400 bolts and added new structural components.
In the next two to three months, shock absorbers would be installed at each end, and monitoring equipment attached so the agency could collect data on how the bridge was performing.
''We've changed the dynamics of the bridge and how it's designed to move, so we want to keep an eye on things.''
Steel bridges were becoming less common in New Zealand, and the project had involved two years of research and design on how best to bring the bridge up to 21st century standards.
''It's required a lot of technical input from experts around the country.''