Transmission Gully figures don't stack up

02:15, May 15 2012
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BEST CHOICE?: Will traffic volumes between Wellington and Kapiti rise, justifying the Transmission Gully route, if petrol doubles in price in the next decade?

The Protection Agency has given draft approval to Transmission Gully. But is this project a good use of a billion dollars when other government spending is being cut and the Government is in deficit?

Essentially, the justification for Transmission Gully boils down to a projection that 1500 more cars will be trying to go between Wellington and Kapiti each day in 2026; a 15 per cent increase.

So, we're talking about spending $1 billion to ease congestion caused by at most 1500 cars, a tiny fraction of road traffic in the Wellington region. It's using a sledgehammer to crack a nut.

Indeed, the official business case says the benefits of the project would be just $600 million, far less than the cost. In other words, the Government's own numbers say Transmission Gully would cost $400m more than it's worth. And that's over-optimistic.

First, it's not likely that traffic volumes from Kapiti to Wellington will actually grow that much.

In the past decade there has been just 2 per cent growth in traffic on this route, and it has actually fallen 1 per cent in the past five years.

The International Monetary Fund says oil prices will double in the next decade, leading to $5-a-litre petrol. A daily commute to and from Paraparamu in a typical car already costs $100 a week. Are traffic volumes going to grow as that cost doubles?

People will seek alternatives to such an expensive commute  like using public transport if it's available, car-pooling or living closer to their place of work.

Second, if we do need to manage some additional peak-hour demand on this route, there are more cost-effective ways than bulldozing a four-lane highway through 27km of extraordinarily rough country.

The Kapiti rail route, for example, is already extremely popular. It could carry many more people if the Government invested in making it more frequent and reliable.

ADDING capacity to the existing rail line has a much lower marginal cost than expanding road capacity, and is a practical option that would get cars off the road, making it safer and relieving congestion.

Not everyone has to use the train to benefit from more people using it.

The other justifications for Transmission Gully also don't add up. Being stuck in holiday traffic for a few hours a year is frustrating but not something the country can afford to spend $1b on.

And Transmission Gully wouldn't be an alternative route for freight or emergency relief in a disaster because its grade would be too steep for heavy trucks.

It comes down to choices. The National Government is planning to spend $14b in the next decade on a handful of highway projects, including Transmission Gully. To achieve this, it is spending very little on anything else  funding has been capped for public transport, road safety, walking and cycling, road policing, and even maintenance and renewals of existing roads through 2022.

Yet the motorways it is prioritising all have poor business cases, where the benefits exceed the costs only under optimistic, unrealistic assumptions.

We could, instead, use that money on projects that move more people and goods (rather than just vehicles), and spend more on targeted safety improvements. This would deliver real benefits to New Zealand's economy.

We don't have infinite money to spend. We have to make wise choices with what we've got. Even if it was mooted a century ago, Transmission Gully just doesn't stack up today.

Julie Anne Genter is the Greens' spokeswoman on transport