Since Auckland Transport and NZTA decided in the middle of last year to rule out Heavy Rail as the best way of serving the Airport with rapid transit, there has been a lot of ongoing consternation from many about this decision. The comments threads on posts about this topic are always long, sometimes enlightening, but also a lot of people seemingly talking past each other.

In general, it seems that most people broadly accept that a heavy rail link to the Airport from Onehunga is too expensive and too difficult. There remains some discussion about whether extending rail from Otahuhu is a viable option – Patrick blogged about this once – although many of the cost issues would be similar to the Onehunga option and the impact of such a route on housing in the area seems like it would be very significant. But most of the talk is about whether a route from Puhinui might be the best idea, this is also a common comment we see in other media. This was looked at in earlier phases of the Airport Rail project, with a few different alignments being examined:

As a branch line off the current Southern Line, presumably if you built this option then either some trains that are currently heading south along this line will either head to the Airport instead of their current destinations of Manukau or Papakura, or further services would need be added. This would mean something like what’s shown below:

This option obviously throws up a few questions:

What are the implications of running more trains on the southern line?

This is already the most constrained part of the rail network. Both the southern & eastern lines overlap between the Westfield and Wiri junctions, but these passenger services also overlap with the busiest section in the country for freight trains as there are shuttles from the Port of Auckland to their inland port at Wiri plus longer-distance trains heading to Tauranga or south of Hamilton. Clearly we’re going to need four-tracks along this whole section for this to work.

Furthermore, even taking freight out of the equation (say through dedicated tracks), there is still only so much capacity available across the rail network – CRL can increase this but only to a point. With Manukau already on its own branch line, another branch to the airport will mean we inevitably have to choose between running a limited number of trains to either the Airport, Manukau or Papakura. In effect, do we want three averagely serviced routes or two well serviced routes and with the way ridership continues to increase, we’re going to need all the capacity to Manukau and Papakura we can get in coming years.

How do trains connect with the North Island Main Trunk at Wiri?

Related to the above, this is a very messy area when it comes to railway tracks. There’s a lot going on here with the southern line branching east to Manukau just north of the motorway while immediately south of the motorway we have, the electric train depot to the west of the main line and the Wiri inland port to the east of it.

Auckland rail network is already constrained by the number of flat junctions it has, which makes timetabling services so they don’t suffer significant delays extremely difficult. As it is, the movements around the Wiri junction can cause issues and so adding another junction in so close would only exacerbate the issue further, both locally and across other parts of the network – for example a train held up at Wiri might go on to delay other services at Newmarket and Quay Park. Any additional branch line would almost certainly require significant junction infrastructure in the area to preserve the chance of having any reliability and that won’t come cheap.

One of the key reasons why Auckland Transport ended up preferring light-rail to heavy rail was because of what happens within the Airport’s boundary itself. The AT Board paper highlighted this issue:

“the heavy rail alignment is also significantly different within the airport precinct when compared to other rapid transit options. It requires tunnelling and an underground station to serve the Airport terminal. The different alignments have made the intent of the sub-regional strategy (to progressively develop up to heavy rail) problematic for Auckland International Airport Limited (AIAL) as they now have to hold two different routes over their land holding (one for light rail and one for heavy rail). This has prompted the AIAL to request clarity on the corridor as it impacts their development plans.”

A number of different heavy rail alignments were looked at as part of the business case work. With the “red” option being the best. A link to Puhinui would probably more closely follow the green alignment, before continuing eastwards to cross the Pukaki Creek. The property impacts of this alignment are pretty obvious in the map below, while the station itself is pretty problematic given AT/NZTA have already let the Airport company know that they prefer light-rail and therefore the Airport no longer is planning its development around providing for a heavy rail corridor.

Even if you “could” build this line, should you?

Hopefully the points above have highlighted that, contrary to popular belief connecting to the heavy rail network at Puhinui isn’t really the “easy option” that it’s often made out to be. There would be extensive tunnelling within the Airport, there would be major and very complex track work around Puhinui to link in with the existing rail network and there would need to be substantial additional track infrastructure on much of the southern line to provide for these extra trains. That all adds up to a lot of money, ultimately for an option which only adds one train station onto the rail network.

One of the big advantages of the light-rail option is that you’re extending rapid transit to a pretty large chunk of Auckland, not just the Airport. Mangere, Mangere Bridge, Onehunga, Hillsborough and Mt Roskill all benefit significantly from the light-rail scheme as they gain access to fast, reliable, congestion free public transport for the wide variety of trips people take – not just for comparatively rare Airport passenger trips.

Ultimately I think the Puhinui option is not a great idea. It’s not as easy as many people think, especially because of the challenge of providing for a heavy rail corridor within the Airport and connecting to the southern line in a very busy and messy part of the rail network. Because it’s not easy, that means it’s likely to be quite a lot more expensive than you might think. But my main problem with this option is that it over-emphasises trying to serve Airport passengers, to the cost of everyone else. Analysis suggests over and over again that most people using rapid transit to the Airport in the future will be workers, not travellers. There wouldn’t be a direct service between the Airport and Manukau, or between Airport and areas to the south of Puhinui (unless you want to end up with really complex and messy, low frequency, service patterns). And huge chunks of southwest Auckland would miss out on gaining access to rapid transit.

This isn’t to say that we shouldn’t provide a rapid transit link from the Airport heading east. Doing so is clearly a no-brainer, but here it seems a busway through to Puhinui, Manukau, Flat Bush and Botany – with a really good interchange at Puhinui with the rail line – seems like a vastly more sensible option, and one that can be implemented much sooner too.

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