Heavy deemed most viable especially via Otahuhu
The Local Government Official Information and Meetings Act (LGOIMA) request I sent to Auckland Transport last month on Airport Rail came back yesterday.
You can see the LGOIMA answer with the links below:
The 2011 Scope and 2016 Business Case studies are at the bottom of this post.
Long story short according to the LGOIMA the heavy rail to the airport via Otahuhu option never made it to a more extensive study in 2011 as it was ranked fourth (of seven) in the short-listed project list. Light Rail (as is being touted today in 2016) came in at fifth place but has Auckland Transport pushing it as their favour option.

Red = LRT proposal by Auckland Transport
Black = Heavy Rail Route proposal
Black dash = Via Mangere route to Airport instead of Onehunga
Yellow = LRT to Manukau as part of Botany Line or Heavy Rail to Manukau
For continuity with the documents I will be referring to the seven options as the packages.
The seven packages were:
I have added outcomes, ranks, costs (2010 prices) and the Benefit Cost Ratios for each of the seven packages.
As it can be seen heavy rail takes the first four in favoured viability with light rail coming in at fifth but Auckland Transport want to continue with the fifth best option rather than the better options heavy rail has always provided.
2016 and changes
With the East West Link at Onehunga making it difficult to bring down both heavy and light rail from the City Centre to the Airport, and the Panuku Development Auckland question (Auckland’s Centre of Gravity Moving South? Part 18 of the #TransformManukau Series) dealing with Auckland’s centre of gravity moving from the Isthmus into South Auckland I firmly believe all seven packages should be tested again along with light rail line from Botany to the Airport via Manukau so see how they stack up with the changes triggered by East-West and the Panuku question.
The 2016 business case study which favours light rail over heavy (despite heavy beating out light rail in the 2011 report) I believe does not factor in the Panuku question properly. With land and house prices accelerating on the Isthmus people and for that matter businesses will usually seek out cheaper location to live and establish employment bases. Regardless of the Unitary Plan Southern Auckland has already seen people and businesses migrate from the Isthmus into the South as the South offers better housing, and establishment of business opportunities on a nominal dollar for dollar value. Furthermore while people and businesses (especially industry) are migrating to Southern Auckland we are seeing the spill over of this migration into the Waikato and Tauranga with people commuting into Auckland for work from those other locations. Given State Highway One and the rail line (Southern Line) afford rapid access into and within Southern Auckland establishing a residential or industrial base in the Waikato is not a silly idea.
The migration south out of the Isthmus will place further importance on Manukau City Centre as a commercial and civic hub while the Wiri and Airport industrial complexes will continue to expand and strengthen in economic clout.
To make matters more interesting most airport complex workers come from South Auckland (Manukau, Papakura and further south):

Source: Auckland Transport
Given Southern Auckland’s increases in population and employment bases those above numbers are only going to get higher with commute pattern trends.
Thus the question is why is light rail favoured to the Isthmus when it has a low BCR and misses the bulk of where the workers come from to the Airport?
Heavy rail to the airport via Otahuhu is the universal connection allowing access by rail to Central Auckland (existing rail network), West Auckland (existing rail network) the North Shore (via the North Shore Line and existing rail network) and South Auckland (existing rail network and busses feeding into Manukau Station from Botany). Back up the via Otahuhu option with the Botany Line from Botany to the Airport via Manukau and we get a dual connection that while both service the airport they serve in different functions.
The Botany Line captures South Auckland, the Waikato and Botany areas (transfers for South Auckland and Waikato would be done at Puhinui between the heavy and light rail lines) while via Otahuhu captures everything north of Otahuhu while still allowing access from the South giving us much redundancy capacity on a key link.
So if I were the new Council after October 8 I would be starting the entire Airport Line study AGAIN through retesting all seven 2011 packages through the new variables especially with the Panuku question factored.
No point building a light rail line north when the bulk of your patronage comes from the south!
2011 Scoping Exercise
2016 Business Case Study