It would be incredibly short-sighted if KiwiRail replaces its 15 main trunk electric locomotives with cheaper diesel-powered engines.

But that's exactly what the state-owned rail company is expected to do this week.

It probably doesn't want to do it, but pressure from the Government to be a profitable commercial operator will force it to.

It's a huge leap backwards. It makes a mockery of the Government's rhetoric last week when it promoted Electric Car Week and claimed the future of transport is electric.

Here's what Transport Minister Simon Bridges said: "We want to encourage New Zealanders to go electric because the benefits are clear. They're cheaper to run than petrol or diesel vehicles and, because they're powered by our abundant renewable electricity supply, they'll reduce the amount of emissions that come from the country's vehicle fleet."

Now, the company of which he's a shareholding minister is poised to announce it's ditching electric trains for Chinese-made diesels.

It defies belief.

Robert Muldoon's National Government electrified 411 kilometres of the North Island main trunk line between Hamilton and Palmerston North in the 1980s as part of his 'Think Big' programme.

Now the National government of 2016 wants to diesel-ify the line.

It will make Muldoon's $250m electrification project redundant.

Its estimated KiwiRail will burn through an extra 8 million litres of diesel every year if it stops using the electric part of main trunk network.

Yes, new diesels are cheaper up front. But new electric locos will be more cost-effective over time. They're faster, and they can haul heavier loads.

The Government should be extending the electric network, not mothballing it to save a few dollars in the short term.