Southern Line, Auckland

From Britomart to Newmarket, Southern Line services use the Newmarket Line, then follow the North Auckland Line to Westfield Junction, and from thence onto the North Island Main Trunk (NIMT) line as far as Pukekohe, the terminus of the Southern Line. In its entirety, this line follows the original 1875 North Island Main Trunk route between central Auckland and Pukekohe.

The line, originally single-tracked, was duplicated, piecemeal, between 1909 and 1939. In 1915, the original single-track Parnell tunnel was bypassed by a twin-track tunnel. The older tunnel can be seen alongside the current one, between Parnell station and Newmarket Junction.

A future Third Main Line is envisaged as part of the Wiri to Quay Park project announced in 2017, which is to start in 2020 and be completed in 2024. It is expected to ease congestion on Auckland rail lines by allowing "through" trains to pass stationary trains at stations, improve rail freight access from the Port of Auckland to the Westfield yards and allow more frequent passenger and freight services.[1][2] The new line would be between Westfield and Wiri.

These improvements will avoid an estimated 175,000 annual freight movements on the state highway network. Work is expected to begin at the end of 2020 and will be divided into four areas outlined below. The $315 million funding package for these works was announced as part of the Government's New Zealand Upgrade Programme.[1]

In 1930, the Westfield Deviation opened a new eastern route for the NIMT between Auckland and Westfield via Glen Innes. The route between Auckland and Westfield via Newmarket then ceased to be part of the NIMT. The portion between Newmarket and Westfield became part of the North Auckland Line (NAL), which runs between Westfield and Whangarei.

The Southern Line suburban services continued to run on the older route. A new line, called the Eastern Line, was introduced for services on the new route. While the Eastern and Southern lines have a different route between Auckland and Westfield, they share the same tracks between Westfield and Puhinui station.

New stations have been proposed at Walters Road and Drury, and are currently being sought by the Papakura Local Board.

Suburban services are operated by Transdev under the AT Metro brand.

The following section of unelectrified track is served by a diesel train shuttle service. Papakura is the transfer hub between services.

• Public transport in Auckland
• List of Auckland railway stations