The government's move to start the rail loop in Auckland two years earlier than planned undermines past promises, generates new political risk and creates an unlikely hero

So, sometimes it's useful being a lame duck.

The government's announcement that it will allow work to start on Auckland's central rail loop (CRL) in 2018, rather than 2020 (it's previous and equally arbitrary start date) is a huge relief for Aucklanders who feared that the project may not just be stalled, but actually abandoned as with public transport plans developed under National governments in the 1950s and 1970s. It seems, finally, the government is entirely and publically on board in principle.

But the fact remains this is still a major u-turn for National.

The government has been insistent that 2020 was the start date and no earlier; the government said the project would not start until patronage and CBD employment figures had been met, yet it is now over-riding its own criteria (the employment goals have not been achieved); and just five months ago National signed a Transport Accord with Auckland Council saying it would take a year to achieve "alignment" and "agree on an approach to develop the city’s transport system". Now, they're pushing ahead unaligned and not having resolved the 30 year plan.

When talking about the potential for an accord back in May last year, Simon Bridges' stance was that he wanted to see "less iconic big projects and more smaller-scale projects" to deal with Auckland congestion. Yet the big money is now going to more big projects.

So while this is the right call for Auckland six years late, the decision is piecemeal and makes a mockery of National's own process.

There are, of course, numerous reasons for this. Most obviously, Key and Joyce are not ones to stay on the wrong side of public opinion for too long, and their unpopular position put a fourth term at risk. Elections are largely won and lost in Auckland, and they had come to be seen as the men standing in the way of progress on Auckland's second biggest gripe – congestion. Rail patronage growth has also become impossible to ignore and the start of the year is a good time to clean the slate and look active.

Further, as Christchurch slows down, the economy needs some more 'big jobs' to maintain growth; the CRL is an obvious pick. I've been writing for most of National's time in office that the availability of cheap money made this a ripe time to take on some big infrastructure projects, and it seems, after the Reserve Bank joined the chorus last year, that's finally become obvious to them as well, if only in a commitment to the CRL and – you guessed it – more roads.

Business leaders in Auckland have also been pressing their blue mates to act for some years, but the need for commercial certainty by big businesses and – notably – big developers along the CRL route I'm sure was significant in the timing of this move.

But amidst all these reasons, I think it's telling that National is dealing with a lame duck mayor; giving Len Brown this win costs it nothing politically, precisely because Brown is so weak. In fact, it's more appealing for National to allow Brown to claim credit for shifting the government's position than for them to move on Phil Goff's watch.

Brown's greatest failure and subsequent political demise has, ironically, ensured his greatest legacy and made it easier for National to move early. Yet undoubtedly, it's under Brown's leadership that Auckland has been able to force Wellington's hand.

Yet some big, chunky politics remains: How to pay for this plan. And not just on the council's side. The government has to figure out how this project impacts its debt promises.

But just how the council raises its part of the cash remains hugely contentious, and National has some slippery roads to negotiate. It is sticking to its philosophical opposition to congestion charges, which has already forced the Council to introduce a "transport levy" (aka raise rates). Now it's saying, as it did with Christchurch, that the city will have to sell assets before the government allows it to introduce congestion charges (which would require a law change). This is a dicey position, in that it risks both blame falling on Key and Co and philospohical stalemate. While National philosophically opposes congestion charges (and fuel levies), Auckland Council philosophically opposes selling significant assets.

It's again Wellington telling Auckland what to do. That doesn't go down well in the big smoke and ties the government to any delays. They cop the blame. Second, does National really want another asset sales fight heading into election year. Because be sure that Phil Goff (and his former Labour colleagues) will happily give it one.

National has manouvered its way out of one vote-losing blind alley. But it risks driving itself into another.