"The work will be completed in stages, with the first objective being able to carry hi-cube containers through the tunnels between Whangarei and Auckland by Christmas."
Being able to carry hi-cube containers would also allow freight that can currently only come in and out of Northland by road to instead go by rail. That additional transport option could help cut transport emissions and reduce the number of trucks on the roads.
Miller said KiwiRail was committed to ensuring Northland benefited from the upgrade project, with a focus on using local contractors and suppliers where possible.
Local firm United Civil Construction has the contract to replace two of the bridges, all the ballast materials for the track upgrades are being supplied by Clements in Whangarei, and Busck, also in Whangarei, is supplying thousands of concrete sleepers.
Next year KiwiRail will continue to make improvements to the Northland Line, including reopening the mothballed section of line between Kauri and Otiria and building a container exchange at Otiria.
State-Owned Enterprises Minister Winston Peters said at least 200 contractors and staff would be needed to undertake the upgrade work and KiwiRail would be using Northland people and businesses wherever possible.
"That will see tens of millions of dollars going into the regional economy, creating jobs and spending that will help Northland recover from the lockdown and impacts of Covid-19," Peters said.
"We're making sure that Northland has access to the same rail services that other export regions have had for decades but this substantial government investment will also help boost Northland's economy right now."