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New tunnel built in a dash

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It may seem strange to build a shiny new rail tunnel and then bury it. But that's all part of the plan to keep motorists safe as part of the State Highway 1 Dashwood Overbridge Realignment safety improvements.

Rail tunnel.Transport Agency Marlborough Roads manager Frank Porter says the project has reached a major milestone with the completion of the rail tunnel that will bypass the aging Dashwood Overbridge and enable motorists to pass over the highway on a straighter, safer alignment.

Mr Porter says the tunnel, which took 15 weeks to build, will be buried over the next two to three months and then the new road built on top.

"The team have done a sterling job, and they deserve a huge pat on the back for getting the tunnel finished a full week early. It's great to see the new shiny new tunnel out there in the open, but blink and you'll miss it - it'll be under a pile of dirt soon so we can whack the road on top of it."

The tunnel is built to strict KiwiRail requirements, and the work was specially programmed to ensure it didn't interfere with train schedules.

Strong progress is also being made on the 2km realignment of the road, which will ensure straighter, high-visibility approaches to the new overpass and the easing of a number of tricky curves on either side. Work will quieten down over winter and then ramp up again in spring, with the project due to be completed midway through next year.

Mr Porter says the project is the largest highway construction project in Marlborough since the new Awatere Bridge was built in 2007.

Tunnel facts:

  • The tunnel is called a "multi plate tunnel", and is made up of 141  5mm thick galvanized steel plates
  • It's 54m long and early 8m wide
  • It's held together by over 10,000 bolts
  • Construction took place while the South Island Main Trunk Line remained operational, co-ordination with KiwiRail ensured there were minimal disruption to train movements
  • Tunnel chosen instead of a bridge as a cost effective solution due to the sharp angle between the road and rail line
  • Designed to the latest standard, including requirements for earthquake resilience

For more information please contact:
Anthony Frith
Media Manager – Central
NZ Transport Agency
T:  04 894 5251
M: 027 213 7617
E: anthony.frith@nzta.govt.nz

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