Those 10 promised bridges now four

The one-lane bridge at Kaeo is still on the dwindling list for upgrading. Photo / Michael Cunningham

Three of the 10 bridges that the National-led government promised to two-lane in the 2015 by-election cannot or should not be built, and there are no firm plans for three more, according to NZ Transport Agency documents.

NZTA has found no economic or safety reasons to build three of the bridges, while environmental reasons outweigh any benefits.

Transport Minister Simon Bridges has reaffirmed his 2015 commitment, however, and has promised that the bridges will be built, with the exception of the Darby and Joan ramp in the Waipoua Forest, which protects the root structures of two giant kauri it passes over.

"We hadn't really thought about those conservation issues sufficiently, but I think we would struggle to get consent," Mr Bridges said.

Meanwhile National lost the by-election, but undertook to stand by its promise to two-lane the bridges, which were not on the NZTA's list of roading project priorities.

NZTA documents show that the Minister was told in 2016 that four of the bridges would be under way by 2018, with work on two of those now expected to begin this year.

Those four are expected to cost around $60 million, well up on the original estimate of $32-$69 million for all 10.

National's candidate in Saturday's general election Matt King said he had been told that consents were about to be granted, allowing work to begin at Matakohe, Taipa and Kaeo.

"I tell everyone but they just don't believe me," Mr King said.

"Unofficially, I know what's going on. If I had a magic wand I'd say, 'Just put the press release out now'."

Work is expected to start at Taipa later this year, followed by Kaeo next year.