[2][3] Scroggy Hill between Glen Eden and New Lynn posed a major issue for trains, as the gradient was too steep for many to traverse.

[1] By the early 20th century, an intensive suburban service ran between Auckland city centre and Henderson, with some mixed trains progressing to Helensville via Waitakere.

At the same time, the stations at Westbrook, Croydon Road, and St George's Street were closed to suburban traffic on a trial basis[5][6] that was later made permanent.

In 1997, as the DMUs stimulated increased patronage, work was undertaken by Auckland Regional Council to extend platforms so that longer trains could be accommodated.

[7] To enable more frequent services, construction began on 9 April 2004 to double track the line between Mount Eden and Morningside.

[8] When this new track entered service, a new timetable was introduced on 14 February 2005 with more frequent trains between Britomart and Waitakere, particularly during peak periods.

[18] From the completion of the electrification of Auckland's suburban network in July 2015, services ceased on the non-electrified section of track between Waitakere and Swanson stations and were replaced by buses.