Prime Minister Jacinda Ardern taking buggy ride on Auckland's $4.4b City Rail Link

Prime Minister Jacinda Ardern is going on an electric buggy ride today for a first-hand look at Auckland's $4.4 billion City Rail Link.

The country's largest ever transport project is nearing the end of the tunnel boring phase and under the spotlight over a pending cost blowout and the completion date being pushed out from 2024 to 2025.

The CRL is a 3.4km twin-tunnel underground rail link connecting the existing Britomart rail station with the Mt Eden station. Two new stations are being built along the route, one in the city called Te Waihorotiu station (Aotea) and the other at Karangahape Rd, called Karanga-a-Hape station.

Once complete in 2025, the CRL will increase capacity into the central city on the rail network from 15,000 people per hour to 27,000. Before it can reach full capacity of carrying up to 54,000 passengers an hour, a further $7.5b needs to be spent on upgrading the wider rail network across the city.

City Rail Link Ltd cheif executive Dr Sean Sweeney. pHOTO / Greg Bowker

KiwiRail and Auckland Transport are currently developing a business case for this work, including an update of the costs to upgrade the network and when the investment will need to be made.

The work involves additional tracks and trains, lengthening platforms for nine-car trains, removing all level crossings on the southern and western lines and a signalling upgrade.

Auckland mayoral and council candidates have recently called for City Rail Link Ltd to open the books on the new cost for the mammoth project before next month's local body elections after statements from CRL bosses and the Auditor-General John Ryan that the cost is set to increase.

City Rail Link Ltd, the body set up to deliver the project, is still working through a claim from the Link Alliance, which is responsible for delivering the main works, for Covid-related matters and set to announce the new cost at the end of the year.

The CRL is jointly funded by Auckland Council and the Government.

CRL Ltd chief executive Dr Sean Sweeney said the tunnel boring phase is expected to be completed this month and works have started on the tunnels' fit-out.

This includes a vast array of equipment and materials, including 16km of rail and more than 1500km of cable.

Artis impression of the Karanga a Hape station on Mercury Lane, just off Karangahape Rd.Photo / Supplied

"These important milestones bring the CRL project into sharp focus and we will soon literally see the light at the end of the tunnel," said Sweeney.

As part of the next project phase, a System Integration Facility (SIF) has been established to integrate CRL sub-systems into a new Auckland rail network operating configuration, with state-of-the-art software and hardware already purchased, he said.

Sweeney said rail tracks are on site and being prepared for laying in the tunnels, as well as sleepers, electronics, safety systems and other essential componentry.