One of the key things that I think attracts some people to the idea of an Airport-Puhinui rail spur is that it seems, intuitively, to be a relatively easy and therefore cheap piece of infrastructure to build. After all, it’s not that far and most of the land between the rail network and the Airport is currently undeveloped farmland. Should be easy, right?
This conclusion is, however, overly simplistic. At each end of this spur, there are some in incredibly complex arrangements that will be required.
Looking at the connection between the rail spur and the rest of the rail network, the map above shows a whole heap of options that were looked at in earlier work. All these options need to work around the environment and an area that’s heavy with other transport infrastructure, including:
- The electric trains depot
- The Wiri Inland Port
- The Manukau branch line
- The South-Western Motorway
How you connect with the rail network also has some important implications for service patterns. Most of the talk about this line has been that it should focus on providing a fast (express?) link between the city centre and the Airport. So this suggests a north-facing connection, much like the red “S1” alignment in the map above. This means there would not be a direct link to Manukau or between the Airport and areas further south. It also obviously means that the capacity of the Southern Line north of Puhinui now needs to be split three ways – to the Manukau Line, the Airport spur and the rest of the rail network to the south.
As Jarrett Walker explains, branch-lines aren’t great as they dilute frequency or create a huge detour. For example, San Francisco a version of this situation, which creates all sorts of service problems – even though the Airport is only slightly off the main line.
In the Congestion Free Network we provide access to the Airport from two big corridors – one heading to the city via Mangere, Onehunga and Dominion Road, and the other heading to Howick via Puhinui, Manukau and Botany. The official plans in ATAP are essentially the same.
With this plan you still have a one seat ride to the Airport from the city, via light-rail. But you also have a one seat ride from the Airport to a huge chunk of east Auckland – and a quick connection at Puhinui to anywhere on the rail network. Without any complex new track connections.
Looking now at the other end of the line – the Airport itself. Under the proposed spur it seems that two stations and a rather odd loop are planned:
Just as an aside, this is a very strange alignment within the Airport, for a couple of reasons:
- The Airport is literally in the process of designing a combined international/domestic terminal, to be open around 2022. This means there wouldn’t need to be two stations – you would have thought the proponents of this rail link might have at least read the Airport’s master plan.
- Given the section of the route within the Airport needs to be tunnelled, it seems very strange to build an expensive loop rather than just a stub-ended line like at Manukau. This approach basically doubles the length of tunnelling required and would only be needed at very very high frequencies.
Getting back to the main point though: threading heavy rail through the Airport is hard. Earlier plans for heavy rail (which largely focused on a link to Onehunga rather than to Puhinui) included a lot of tunnelling.
A whole bunch of different alignments were looked at in some detail, with their costs generally around three times as much as light-rail due to the tunnelling requirements.
Furthermore, even at this cost-differential you only got one heavy rail station (right at the terminal itself, as per the image above) whereas with light-rail you could quite easily get another station to better serve the growing business park. Looking at the map above, a Puhinui Link would follow the green alignment from the Airport terminal before emerging somewhere before the inlet and crossing over in a bridge. Because of the significant property impacts within the Airport (the green line runs through a whole pile of buildings and across a number of key routes) you’re looking at a 1.6 km long tunnel even without the weird loop in the Herald image earlier.
By way of contrast, light-rail can make its way through the Airport area much more easily.
It only needs one short section of tunnel, underneath the future northern runway, which would be shared with SH20A. It then runs at grade along John Goulter Drive and Manu Tapu Drive right into the heart of the terminal.
Overall, the complexity of delivering a heavy rail spur to the Airport from Puhinui is not the deciding factor in our preference for light-rail. As I explained last week, we much prefer light-rail because it does so much more than just serve Airport-City trips – it will help fix many of Auckland’s most severe housing and transport problems. But it does annoy me when people say this Puhinui spur would be easy – it wouldn’t be.