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It pulled a young nation to its feet 100 years ago. Now the North Island Main Trunk railway is being enlisted for service in an epic 21st century struggle.

Once a despoiler of prehistoric forests in return for the economic and social prosperity it delivered, the trunk - with its giddying viaducts and the engineering masterpiece of the Raurimu Spiral - is being looked to as a environmental lifeline.

Under renewed state ownership, the successors to the "iron horses" central to 19th century Colonial Treasurer Julius Vogel's nation-building ambitions are being harnessed to Government hopes of halving per capita greenhouse gas emissions from domestic transport by 2040.

The North Island trunk, over which the first train trundled into Auckland from Wellington 100 years ago yesterday carrying politicians eager to greet a "Great White Fleet" of American battleships, opened the previously impenetrable Maori stronghold of the King Country to European settlement and economic development.

Rail travel became the norm for the first 50 years of the line, linking communities and boosting industries until increased car ownership, the lifting of restrictions against freight-haulage competition from trucks, and cheaper air services signalled the end of its first golden age.

Now the country's leaders are invoking the pioneering legacy once more, dusting off the family silver at a time when volatile fuel prices are raising doubt over the future of long-distance travel by the masses in private cars and aircraft.

After a near-death experience just two years ago, when former rail operator Toll threatened to ditch the last remaining passenger trains between Auckland and Wellington, the Overlander daytime service is starting to thrive again.

It is running close to capacity of just over 160 seats on many trips, raising hope that its daily services in the December-April tourism peak may soon be restored to the other months, when it operates only on Friday, Saturday and Sunday.

A leading travel writer gushed about the Overlander in Britain's Guardian newspaper this year as offering one of the world's best-value scenic rail trips.

The Government's $690 million buyback of the national rail fleet and the Cook Strait ferries from 15 years of private ownership was followed quickly by an $80 million budget for the renewal of rolling stock such as the Overlander's 1930s carriages and upgrades to locomotives as a down-payment on a carbon-busting future.

Officials say that is just to keep services ticking over, and not to prejudge growth plans being formulated by the new state enterprise KiwiRail, as the Government prepares an investment budget of hundreds of millions more dollars.

The do-up could also free existing carriages for a resurrection of some regional services axed by the former Tranz Rail in 2001.

The Government has separately earmarked $400 million for a five-year upgrade of rail tracks bought back from private ownership for $1 in 2003.

Prime Minister Helen Clark said at the launch of KiwiRail that high oil prices and a sense of urgency in the fight against climate change were making many nations look afresh at rail as central to their 21st century economic infrastructure "and so must New Zealand".

She noted that diesel trains were four times more fuel-efficient than trucks for hauling freight, and electric locomotives 10 times so.

National has promised not to reprivatise the railways or other state assets in a first term back in office.

Former National Prime Minister Jim Bolger, appointed by Labour as chair of KiwiRail's board, defends his past administration's sale of the rail in 1993 when oil was five times cheaper than now but says he hopes his old crew will invest heavily in the business if it wins back the Treasury benches.

Community leaders in Waikato and Bay of Plenty are becoming eager for regional services to tap back into the main trunk.

Rail authority Bob Stott believes electrified rail tracks between Palmerston North and Hamilton - from a $260 million "Think Big" project of the 1980s - must eventually be extended at both ends to Auckland and Wellington, and to the Port of Tauranga for freight traffic on operational and energy efficiency grounds.

"Any form of energy can be converted into electricity and piped to the train," he says. "Power stations can use water, wind, coal, gas or even old gumboots - so if we're stuck without oil, there's always electricity."

Electric trains can also draw more power for faster acceleration out of stations and sharp bends than diesel engines.

"The whole power station is behind an electric locomotive, whereas with a diesel you're stuck with the power that the engine can produce. You don't have the whole of the Waikato power system pushing the train along."

Rail consultant Dr Murray King estimates it would cost $860 million to electrify the tracks between Papakura and Mt Maunganui via Hamilton.

That would cover the country's busiest rail freight routes, saving around 12 million litres of diesel a year and 28,000 tonnes of carbon dioxide emissions.

But he cautions the cost would be almost four times the economic benefit, money better spent elsewhere on improving rail services to attract road freight, making fuel savings that way.

Despite that, he says the introduction of an intensive passenger service between Hamilton and Auckland or hefty diesel price rises could alter his assessment.

King believes a daily commuter train to Auckland could prove viable if it started modestly, such as using old Silver Fern railcars, spruced up for around $3.6 million for a pair of two-car sets.

The railcars would be faster than conventional trains, and manage two return trips a day in just under two hours.

But King says access to the increasingly constrained Britomart Station could be difficult in view of Auckland's rapidly growing rail services, and it may be necessary for Waikato commuters to change trains at Newmarket.

Hamilton City transport chair Dave Macpherson says his council has already set aside money to develop a new railway station, and there is no reason a Waikato-Auckland commuter link could not be even more successful than a popular service between the smaller population centres of Palmerston North and Wellington.

Environment Waikato passenger transport chairman Norm Barker says his region has the highest number of road crashes in the country, and putting more people and freight on to trains may help to tame that unenviable reputation.

Despite Stott's reservations about the suitability of long-distance rail travel for businesspeople, adventure tourism and hospitality entrepreneur Thomas Manning says he is considering the viability of a night train between Auckland and Wellington for that very purpose.

He is now working with a design and engineering team on the possibility of importing two conventional trains for both day and night travel.

He says each train of six Vietnamese-made carriages could be bought for less than the $6.5 million price of railcar sets, and be available by day for tourist and local travellers, before being converted within an hour to sleeper configurations.

"We believe an overnight service would get a significant uptake. A lot of people prefer rail to planes if they can get a good night's sleep."

He is confident conventional trains with modern suspension could chop at least two hours off the 12-hour Overlander trip.

Although Manning considers the rail buyback an inspired move, he believes licensed private operators could offer superior passenger service in return for exclusive access rights to set routes.

Whatever happens, the former Waiouru schoolboy and long-distance rail commuter believes future generations can look forward to celebrating the bicentenary of the North Island Main Trunk in 2108. "Without a doubt, the way the whole world's going from an emissions and costs point of view. Rail has a golden future."


What sort of future trains could travellers expect on New Zealand's rail tracks?

Obviously it depends on investment plans, but rail publisher Bob Stott believes KiwiRail should consider importing quiet electric "tilting" trains such as seen in Queensland and Europe, able to lean into curves like motorbikes and whisk passengers along at up to 160km/h.

"Yes they are expensive, but an aeroplane is expensive, too," he says.

Commuters could zoom from Hamilton to Auckland in little over an hour, plugging in laptops to check email, tucking into breakfast, or snoozing in air-conditioned comfort as cars and trucks disappear behind them on State Highway 1.

Stott is confident the global renaissance of rail will not pass New Zealand by, despite the challenges of rebuilding patronage in an elongated but still little-populated country.

He notes that high-speed passenger trains are starting to bite into short-haul airline business in Europe and that the United States' railways are exceedingly hard-pressed to keep up with demand for freight services.

Stott believes high-speed passenger trains could become popular on many sections of the 681km main trunk - especially between towns without air links.