It connects the North Island Main Trunk (NIMT), which runs from the east into Waitematā via the waterfront, and the North Auckland Line (NAL), which runs between Westfield Junction and Otiria via Newmarket and Whangārei.
The Newmarket Line was originally opened in 1873 as the northern portion of Auckland's first railway to Onehunga via Penrose.
It was part of the North Island Main Trunk Railway until the Westfield Deviation opened in 1930.
[3] Since 1915, it has been fully double tracked after an upgrade of Parnell Tunnel north of Newmarket.
This was part of a big upgrade of rail infrastructure in Auckland, and the Newmarket Station and Junction was included in the stage one electrification of the network.