National is promising to double both the Mt Victoria and Terrace Tunnels in Wellington as part of a $4 billion spend up across the region if the party is elected into government in September.

The Party also wants to create a stand-alone agency to deliver the $6.4b Let's Get Wellington Moving (LGWM) project, which it intends would then transition into something similar to how Auckland Transport operates.

During a speech to the Hutt Valley Chamber of Commerce this morning, National leader Judith Collins outlined the party's transport plan for the Wellington region over the next 20 years.

National is still supporting the current LGWM project announced by the current Government in May last year.

But it's adding back in roading projects that were initially recommended but didn't make the final cut- mainly trenching the Inner City Bypass and doubling the Terrace Tunnel.

The Government scrapped these two significant projects, with Transport Minister Phil Twyford saying at the time they settled on the amount of money that could prudently funded and financed.

National also wants to re-jig the sequencing of LGWM by starting construction on a second Mt Victoria tunnel within its first term, and would legislate for this to happen if necessary.

The $4b is Wellington's slice of National's $31b infrastructure package, which is on top of funding that has already been allocated through LGWM and the New Zealand Upgrade Programme.

Collins said Wellington has talked about transport for too long and the time for "endless and interminable squabbling" was over.

"Let's Get Wellington Moving was designed as a package of investments but Phil Twyford and Julie Anne Genter ignored the recommended investments, removed the state highway projects and pushed the second Mt Victoria Tunnel to 2029 or later. Our package implements what was recommended and what Wellingtonians want," she said.

National wants to start undergrounding State Highway 1 through Te Aro by the end of the decade at a cost of just over $1b.

A second Terrace Tunnel would also start within the decade at a cost of $400 million.

Under the plan, central government would pick up the full tab for the state highway projects.

The current deal negotiated under LGWM is for local councils to pay 40 per cent of the overall package, leaving central government to fund the remaining 60 per cent.

Collins said the second Mt Victoria Tunnel would deliver more reliable travel times between Wellington's CBD, eastern suburbs and the airport.

"Everyone in Wellington wins from having a second Mt Victoria tunnel."

LGWM is the first major investment in the city's transport network in decades but it has faced plenty of controversy.

A letter Associate Transport Minister and Green MP Julie Anne Genter sent to Twyford just months before the package was announced turned into quite the hoo-ha.

The Ombudsman ended up ruling that Genter was entitled to withhold a copy of what's now known as the "secret letter", but a statement she subsequently issued revealed she did in fact ask for mass rapid transit to be prioritised over a second tunnel in exchange for her support.

National's announcement indicated it's plan for mass rapid transit would be buses or trackless trams, rather than light rail.

The big winner from National's policy in the Hutt Valley is $900m for constructing the Petone to Grenada link Rd as part of a new Seaview to Grenada Link Road project.

National would also declare the Cross Valley Link road corridor a State Highway and fully fund the project.

The party has planned to allocate $300m to fund the Greater Wellington Regional Council's investment proposal for new trains to operate services in the Wairarapa and Manawatū.

Regional Council chair Daran Ponter previously sent MPs, ministers and mayors a tin of sardines in the mail to illustrate a rail network on the brink of bursting across the lower North Island.