North Auckland Line

The North Auckland Line (designation NAL) is a major section of New Zealand's national rail network, and is made up of the following parts: the portion of track that runs northward from Westfield Junction to Newmarket Station; from there, westward to Waitakere; from there, northward to Otiria via Whangārei. The first section was opened in 1868 and the line was completed in 1925. The line, or sections of it, have been known at various times as the Kaipara Line, the Waikato-Kaipara Line, the Kaipara Branch and the North Auckland Main Trunk.

North Auckland Line is a designation for the section of track, not a service route. The southernmost portion from Westfield Junction to Newmarket was originally built as part of the North Island Main Trunk railway, with Newmarket serving as the junction of the two lines. The North Island Main Trunk was re-routed in 1930 via the Westfield Deviation through Glen Innes and Panmure. Westfield-Newmarket was then incorporated into the North Auckland Line, and Newmarket-Auckland became the Newmarket Line, which today connects the North Auckland Line to Britomart Transport Centre.

Three passenger lines of Auckland's suburban rail network make use of the North Auckland Line. Southern Line services travel on it between Westfield Junction and Newmarket Station. Onehunga Line services travel on it between Penrose Station and Newmarket Station. Western Line services travel on it between Swanson Station and Newmarket Station.

The North Auckland Line previously continued to Opua in the Bay of Islands, with the section from Otiria to Opua sometimes known as the Opua Branch. It is now owned by the Bay of Islands Vintage Railway but regular operations were suspended in 2001, with resumption on a short section of the line in 2008.

The North Auckland Line was under review as part of KiwiRail's turnaround plan. In 2020, the government announced $109.7 million for upgrades to the line, focussing on rebuilding and lowering the floors of 13 tunnels along the line to enable hi-cube containers. A container terminal is to be built at Otiria.

A new branch line, the Marsden Point Branch, will serve Northport, a deepwater port at Marsden Point, by diverging from the North Auckland Line south of Whangarei at Oakleigh.

In 2023 the NAL was expected to be out of action to at least June after floods in January; (see 2023 Auckland Anniversary Weekend floods), and it was announced that KiwiRail was "progressing" the business case for the new Marsden Branch.