The party has been pushing for the projects ever since, including last month delivering eight petitions - signed by more than 16,000 people supporting the highway projects - to the transport and infrastructure select committee.
The Government's duty minister, David Clark, said the hoardings were "cynical politics", and called National's wishlist a "desperate $12 billion promise on the eve of the last election".
"They were never budgeted or funded, and National couldn't have afforded to build them even if they were returned to office. That's because the entire annual transport budget is around $4 billion a year."
Last week the Government announced it was putting $1.4 billion into a plan to save 160 road deaths and serious injuries a year, aimed at improving 870km of high volume, high-risk State Highways by 2021.
The improvements will focus on median and side barriers, rumble strips, and shoulder widening.
Clark said the same amount of money set aside for the 870km of highway improvements would translate to a 25km-upgrade for one of National's proposed four-lane expressways.
National's MP for Northland Matt King and Associate Transport Minister Julie Anne Genter got into a Twitter spat over the hoardings yesterday.
"Imagine if a 4-lane highway to Whangarei was the only new transport project built for next decade. Millions of people travelling all over NZ could expect no improvement to their daily grind, no safety upgrades any where else... that's the opportunity cost," Genter said.
King replied it was only one of several planned upgrades, and Genter replied: "And how were you going to pay for them? Especially when you promise to discontinue petrol tax rises? Motorways aren't cheap, Matt, and money doesn't grow on trees."
"We would start by not wasting money on fees free or the Jones slush fund for a start," King retorted.
Genter pointed out that neither of those affect the National Land Transport Fund, and King replied that public-private partnerships would help.