Official documents reveal it is likely to take much longer than initially thought to build the roads of national significance.
The Government set an aspirational goal of 10 years to complete most of the seven roads by the 2020/21 financial year.
A Transport Agency briefing to Transport Minister Gerry Brownlee in February said the agency was committed to substantially completing the seven roads by then.
However, based on current funding and revenue projections, it might take three years longer.
It is the first admission that the goal to complete the $10 billion roads might not be realistic.
As late as April, six weeks after the briefing, Mr Brownlee told Radio New Zealand the majority of the new highway work would be completed in a decade.
On Monday, the minister dismissed the Transport Agency's report, saying he remains unconcerned about one paragraph from a 33-paragraph report that is largely positive and a lot can happen in 10 years.
"The first road of national significance project is completed. It was completed in time and under budget, so there are some very encouraging signs there."
Green Party transport spokesperson Julie Anne Genter is not surprised the roads project may take longer, saying that as fuel prices rise, demand for passenger trips and freight is falling and pushing down road user revenue over the decade.
Ms Genter says it is not too late for the Government to shelve some of the projects.