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  • Writer's pictureGrant McLachlan - Stuff - Column

Is it time to tunnel across the Cook Strait?

Considering the state of our inter-island fleet, the cancellations of air and sea travel due to weather and the future demands on utilities, it is time that we examine the feasibility of a fixed link between our two main islands.

Bridges and tunnel technology have improved in both engineering capability and affordability. More recently, this country has invested in megaprojects that have delivered on their goals.

"But what about the cost?" would be the cry by most. What we should be asking is: "What's the alternative?".

Way back in the 90s, I considered that question in a research project. At that time, the English Channel Tunnel, the tunnel and bridge link between Denmark and Sweden, and several bridges and tunnels in Japan linking the main islands were ending construction. Since then, mega tunnels and bridges have been completed in Asia, America, and Europe.

Based on those projects, I have re-examined the feasibility of a fixed link between the North and South Islands of New Zealand.

The best comparison of the growth effect of a fixed link with the Cook Strait is the Confederation Bridge linking Prince Edward Island with New Brunswick in Canada.

Prince Edward Island has a population of 140,000 and New Brunswick has a population of 750,000. The Lower North Island of New Zealand has a population of 725,200 (Wellington and Manawatu) and the Upper South Island of 120,000 (Nelson, Marlborough, and North Canterbury).

Since the completion of the Confederation Bridge, tourist visits have increased from 740,000 in 1996 (the year before the bridge opened) to 1,200,000 in 1997 and stabilised at around 900,000 visitors annually. The bridge has daily traffic of approximately 4000 vehicles. The toll for a two axle vehicle is C$44.50 plus C$7.25 per extra axle.

The Cook Strait ferry service carries about one million passengers and 230,000 vehicles annually.

Between three and four million tonnes of cargo are transported on the ferries - two-thirds by truck and the other third by rail wagon. The revenue from sea traffic alone across the Cook Strait is over $1billion annually.

A tunnel linking the Picton and Wellington ferry terminals would be 66.6km in length. Two bores would be drilled; a smaller pilot/maintenance/escape tunnel and a wider tunnel. The wider tunnel could have separate levels for road and rail traffic.

The Channel Tunnel cost £4,650 billion (two tunnels and a pilot, 1994) and the Seikan Tunnel cost ¥538.4 billion (US$3.6 billion, one tunnel and a pilot, 1988). The Seikan Tunnel has the most similar length and terrain to a Cook Strait Fixed Link.

Based on other similar projects, and considering how much traffic already crosses the Strait, that makes the feasibility of a tunnel very realistic, especially if the tunnel cost could be paid back within 15-20 years - shorter than the Auckland Harbour Bridge tolls were in place.

The government-owned Kiwirail is considering building a new and expensive ferry terminal while its fleet struggles to stay in one piece. Wellington Airport is also looking at extending its runway. The spoil from a tunnel could be used to extend the runway, expand port facilities, and reclaim other land.

"But what about the earthquake risk?" some would say. The Seikan Tunnel linking Hokkaido and Honshu islands in Japan sits in an area prone to earthquakes but has withstood many major earthquakes unscathed. The shortest and most practical route between Wellington and Picton ferry terminals would avoid the Tinakori fault and stay west of the continental fault.

Another factor to consider is the growth in demand for utilities. Currently, only electricity using the HVDC link is shared between islands. A tunnel would allow many more utilities to be shared between the islands.

Rather than dismissing the suggestion of a fixed link, we should at least explore whether it is possible and then whether it is feasible.

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