Carterton Mayor wants a Remutaka Hill road tunnel

AI generated image of a tunnel going through a forested mountain range.

An email supplied to Local Aotearoa reveals that Carterton Mayor Ron Mark is apparently trying to get a road tunnel through the Remutaka Hill back on the regional infrastructure agenda, reigniting a proposal that’s been kicked around in various forms since at least the 1960s, if not even earlier.

In an email to the Programme Director and Chair of the Wellington Regional Leadership Committee (WRLC) discussing the concerns of mayors with the work of the committee, Greater Wellington Regional Council Chair Daran Ponter speculated that one of the causes of their angst about the committee’s work was that some of the region’s mayors were feeling that “they cannot see themselves in the WRLC proposals (e.g. Mayor Mark and his Remutaka road tunnel proposal)”.

As a result of this, Ponter suggests that a Remutaka Hill road tunnel could be a candidate for a feasibility assessment as part of a re-focusing of the WRLC’s efforts. Suggested other candidates for feasibility assessments would include a “North-South Junction”, a “East-West route”, and one or more transit-oriented developments (TODs).

The North-South Junction is likely to refer to the 7km of train network between the old Muri station at Pukerua Bay and Paekākāriki, where there have been numerous proposals to either replace the entire section with twin tunnels, or upgrade the section with double tracking and additional tunnels as required to make this work. As to what the East-West route might be, I’m not entirely sure. The idea of these feasibility studies is to ensure the proposal is worth seriously considering and presumably isn’t possible from either an engineering or economic perspective.

The idea of a Remutaka Hill road tunnel is nothing new, and various proposals for it have been kicked about over the years. The earliest reference I could find online is this clipping from the Upper Hutt Leader in 1967 which includes a map of a proposed tunnel through the hill. That proposal would’ve seen the tunnel start some 292m above sea level (the summit of the road is at 555m) and involved a whole new and surprisingly straight route on the western side of the range.

A slightly more recent assessment carried out by Duffill Watts and Tse considered both a 3km long tunnel running under a significant portion of the range and a much shorter 500m tunnel that would largely bypass the summit. While their report concluded that both tunnels were feasible from an engineering standpoint, the costs would be prohibitive and make the project economically unviable. I’m not entirely sure of when that report was commissioned. The chief advocate for the tunnel at the time was then Wairarapa MP John Hayes (there’s a couple of brief references in Hansard of him mentioning the tunnel from 2005 and 2008 where he claimed it would be cheaper than Transmission Gully and have a positive BCR), and he was MP from 2005 to 2014. Duffill Watts didn’t acquire Tse Group until around 2007. My Dad worked for Tse Group at the time, and then briefly for Duffill Watts and Tse, but as he died last March I can’t ask him when it was.

In any event, while such a tunnel would likely be transformative for Wairarapa, it would be surprising if the economics had improved at all. As an example, Let’s Get Wellington Moving recently put a ballpark figure of $3.1 billion on a 4km long tunnel underneath Wellington. It could very reasonably be expected that even a relatively small 500m long summit tunnel could still be at least $500 million, if not more, and deliver comparatively few benefits in terms of overall resilience of the road.

That being said, Transmission Gully went ahead despite the huge costs involved (costs which are still being sorted out several years after the road opened). Transmission Gully has also been transformative for the Kāpiti Coast and for weekend and holiday periods in improving not only driving times but safety and route resilience too. So if the political winds align you can’t rule something like this out even if the financial and engineering side would be challenging.