There was much speculation over the Deputy Prime Minister's post-Budget announcement in Whangārei about Northland rail being on track, but the train is still sitting in a siding.

Getting the trains running was a matter of the planets aligning at the right time, Winston Peters said.

The big reveal of his address on Friday evening was that the geotechnical and engineering investigation into the Marsden Point spur line was now fully complete and the improvements needed to bring the 100-year-old Northland-Auckland line up to standard would be relatively straightforward.

State-owned KiwiRail was planning to revitalise the Northland-Auckland line, Peters said. The work was well within the normal range of expertise held by local domestic design and construction firms, he said.

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''The message is this - rail is back on track. This is not an empty statement, or hollow words but a statement of fact, figures and, more importantly, the dollars to back it all up,'' he told a gathering of the Grow Northland Rail campaign group and other faithful at mainstreet bar Pure.

Despite the ra-ra mood at the event, the ''facts and figures'' Peters referred to appeared not to apply to Northland's rail development — at this stage, anyway. Northland was not mentioned in specific jobs earmarked for Budget 2019's $1 billion investment in rail, but $300 million is to come from the Provincial Growth Fund for the regions.

''Completing this investigation - giving us a clear idea of where we stand - is important for when the Upper North Island Supply Chain Study and the Ministry of Transport's plan for rail investment are finalised around September,'' Peters said.

''From there the Government will be making decisions about rail investment in Northland.''

His mood indicated there was some certainty already about those decisions.

''You might just stay the planets are about to be in alignment.

''[KiwiRail] now needs to prepare its application to the Provincial Growth Fund (PGF) to get the Northland rail line properly back up and running, and there is not a moment to be lost. We know that without investment, the Northland rail line would have to close in three to five years.''

Also at the event was KiwiRail chief executive Greg Miller, who earlier said 30,000 container loads left Northland by road each year for the ports of Auckland and Tauranga – and rail was missing a huge opportunity to take some of that freight.

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Miller said KiwiRail was already preparing an application to the PGF.

''The spur is a supply chain issue. The 130-year-old, in places, Auckland to Northland line is only a few years away from closing,'' Miller said.

''The choice is to close it or upgrade it.''

He said the consents process for the line alone could take two years.

Peters reiterated that KiwiRail needed to prove a case that improving the rail line would translate into regional growth, better connectivity with New Zealand's largest city, and more jobs.

''We started this process, and signed the Coalition Agreement, because we know the case is compelling in places such as Northland.

''And while difficult to prejudge an application to the PGF, it is hard to see a contrary argument on developing the Marsden Point link, or even a future when the rail links are entrenched to further North to Otiria or through to Dargaville.''

The announcement was followed with the screening of a documentary made by Grow Northland Rail about the need for a revitalised line to Auckland and the Marsden Point rail spur.