BY May traffic will be flowing over the new road and culvert which is replacing the 90-year-old Whakaruatapu Bridge, known to locals as the Skinny Bridge, north of Dannevirke.

Work has been progressing well, with construction on the new culvert and road to the north of the bridge well under way.

A culvert was the safest, least disruptive and most cost-effective solution to replace the current narrow bridge, Neil Walker of the New Zealand Transport Agency (NZTA) Central Region Highways, says

"It is likely the current bridge would not cope with the effects of a significant earthquake. The new road layout and culvert is going to be wider, longer, lower, safer and more resilient than the 'skinny' bridge it is replacing," he said.

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Traffic will be able to use the new road and culvert in May, when the existing bridge is scheduled to be demolished. There will be initial speed restrictions until the road surface is finished.

"We started construction works on this project in October 2014 and the whole project will be complete in September this year. It's been a big job - the project required approximately 150,000 cubic metres of material to be shifted to form the new road alignment," Mr Walker said.

The project also includes a New Zealand engineering milestone, as the culvert is first Super-Cor Arch Culvert constructed in New Zealand.

"This type of culvert was the only option strong enough to handle the weight of the 16m of rock fill that will be above it," Mr Walker said.

The current alignment will be maintained in a safe condition until traffic is transferred to the new road and culvert.

Fast facts:

* The new culvert is 120m long, 6m wide and 3m high, with a reinforced concrete slab foundation.

* The new road level is approximately 3m lower than the existing bridge over Whakaruatapu Stream.

* The existing bridge is 5.79m wide between kerbs. It is a 22m high level viaduct type structure, 58m long with a reinforced concrete deck.