Station to become major interchange
Those who travel the Southern and Manukau Lines in Auckland wouldn’t think much of Puhinui Station. Puhinui current sits in between the larger Papatoetoe, Homai and Manukau Stations all which serve as interchanges in some form. While Puhinui Station serves as a transfer point between the Southern and Manukau Lines its role could be a whole lot bigger within the next decade.
Let’s take a look at Puhinui Station and the surrounds:
Puhinui sits prime on major transport routes to both Manukau City Centre and the Airport complex. There is also sufficient enough land belonging to Kiwi Rail to build a proper interchange at Puhinui Station with four platforms and an extra track free for freight trains to bypass the station. This is made possible with four mains and a loop running through the interchange site. Technically the Fourth Main (the Third Main on the left hand side would be kept clear for freight) would service Platform Three with an extra loop servicing Platform Four as demand allows but none the less we will need four Mains between Wiri and Otahuhu to get best use out of Puhinui Interchange.
The Four Platforms
This is how I have allocated the platforms at Puhinui:

As I noted earlier I have kept the Third Main on the airport side clear of any platforms to allow freight trains to run through the Interchange area unimpeded. The existing two Mains plus the Fourth Main take up Platforms 1-3 to service commuter, airport and inter-city patronage with an extra loop on the Manukau side forming Platform Four if demand ever warranted another platform (such as an inter city train heading south and keeping the other Mains clear given the extra loading time that might be needed).
The yellow is the interchange area while the grey is the bus line to and from the Airport remembering the interchange will need to be able to service Light Rail when the time comes to turn the Southern Airport Line from a bus-way to Light Rail Transit line.

How Puhinui Interchange will look in a wider context. The white lines are the two existing Mains with the black the Third and Fourth Mains in utilisation. You can see where the new platform along with a loop track goes keeping the Third Main entirely clear for freight trains. The Third Main also allows for the electric passenger trains to enter and leave the Wiri depot without impeding on the other three Mains.

This is how Puhinui Interchange would interact with Manukau Station and the Southern Airport Line from Manukau to the Airport. You will also notice that I have added the Manukau South Link back in there allowing services from Pukekohe and Papakura to Manukau directly without a transfer at Puhinui Station. With Puhinui Station set to be a major interchange handling commuter, inter-city and airport traffic, re-directing Manukau passengers away from Puhinui Station through a direct connection to Manukau from the South would ease loading pressures at Puhinui.
So the economics of the Manukau South Link do make a comeback with the Puhinui Interchange and the Southern Airport Line.
As for inter-city trains?
Call for Hamilton to Auckland commuters to get on board rail service
- Friday, 12 May 2017, 11:20AM
THIS ARTICLE WAS PUBLISHED BY HAMILTON NEWS ON FRIDAY, MAY 5TH
Proponents for the establishment of a commuter rail service between Hamilton and Auckland will need to bridge political gaps and unite if the initiative is to gain traction, it emerged last Sunday.
Community group The Rail Opportunity Network (TRON) held a meeting earlier this month in the historic Frankton Hotel adjacent to the railway line the train would traverse as it left Hamilton heading for Auckland – if it came to be a reality.
TRON is a collective of people from a range of backgrounds who have all expressed ongoing interest in bringing the intercity train into operation.
Engineers, railway staff, politicians, tourism organisations and health and safety experts have all entered the ring in support of the service.
Susan Trodden, spokesperson for TRON, was among the key organisers of the discussion.
There was a large turnout, including members of the public, Hamilton business owners and numerous local political representatives.
“It’s quite important we have a good roundtable community discussion on this,” Hamilton city councillor Dave Macpherson said as he spoke on the discussion panel, emphasising that the train should not become party political.
“The growth in the Waikato, from Hamilton north to Tuakau, is phenomenal at the moment and is going to be phenomenal for some years to come.”
Macpherson noted expanding and upcoming residential developments in Pokeno, Mercer, Huntly and Te Kauwhata which he said would all increase the pressure on Stage Highway 1 and the need for a train service to those areas, which could double in benefit to link Hamilton with Auckland.
“A lot of the planners in this area and nationally are actually way behind the 8-ball there. We’re seeing figures coming forward from supposedly reputable planners to the Waikato District Health Board saying the population in Hamilton is only 147,000 at the moment – it was that seven or eight years ago,” Macpherson said.
……..
Full article and source: http://www.newstalkzb.co.nz/news/national/call-for-hamilton-to-auckland-commuters-to-get-on-board-rail-service/
The Tweet below also relevant:
As for the Airport Southern Line?
In red as Option 1

Source: Auckland Transport
Building Puhinui Station out to four platforms when the Southern Airport Line Puhinui Interchange is built makes sense to handle the varied mix of patronage coming through that station.