Only one way in: Unsafe Northland bridge "miraculously" becomes safe

Structural problems with the Waitangi River Bridge on SH10 were discovered earlier this year. Photo / Peter de Graaf

A structural engineer is checking an ageing bridge on State Highway 10 daily for fresh cracks after the closure of SH1 left the east coast route the only major road to Kaitaia still open.

In March this year Waka Kotahi NZ Transport Agency banned overweight vehicles from Waitangi River Bridge, on SH10 just north of Puketona Junction, after a routine inspection identified structural problems.

The agency also put up temporary 50km/h speed limit signs on either side of the bridge.

Overweight trucks were instead required to use SH1.

At the time Waka Kotahi said the deterioration was such that immediate action was required.

However, with SH1 closed by slips at Mangamuka Gorge since the deluge of August 18-19, Waka Kotahi has reopened Waitangi River Bridge to all vehicles.

Drivers of overweight trucks have been instructed to travel at 10kmp/h and straddle the centre line while crossing the bridge.

The only sign of trouble at Waitangi Bridge is a 50km/h speed limit sign. Photo / Peter de Graaf

A Waka Kotahi spokesman said temporary access for overweight vehicles had been reinstated while SH1 remained closed through Mangamuka Gorge.

"The condition of the bridge is being very closely monitored, with a structural engineer checking the bridge daily," he said.

The Northern Advocate understands the problem is cracking of the ageing concrete structure.

Parapara Bridge, on SH10 near the Karikari Peninsula turnoff, has similar issues.

Far North deputy mayor Ann Court questioned how a bridge that had been deemed unsafe for overweight vehicles had "miraculously" become safe again.

There were detours available via local roads if the bridge failed, but they were not suitable for heavy vehicles or the volume of traffic that used SH10.

Kaitaia Business Association chairwoman Andrea Panther was deeply concerned about the effect on Te Hiku, the top of the Far North, if both SH1 and SH10 were closed.

"If one of those bridges on SH10 goes we'll be completely isolated," she said.

It would be possible to use the road around the west of the Mangamukas but that also needed repairs — it was down to a single lane in places due to slips — and was not suitable for large trucks.

The maximum weight of a truck and trailer depends on a number of factors including the number of axles.

A truck 17.4m long or more with at least eight axles can weigh up to 46,000kg, according to Land Transport Rule: Vehicle Dimensions and Mass 2016.