The Edinburgh trams fiasco continues to astonish.

The Edinburgh trams fiasco continues to astonish.

Now it has been revealed a report examining the cost of extending the existing line to Leith and then Newhaven will itself cost up to £400,000.

It seems inexplicable that merely assessing a proposal could cost so much, especially in the context of a city which is under pressure to make cuts.

All the options for Edinburgh's trams have already been assessed, numerous times. Surely the cost of running trams as far as Leith and Newhaven has already been considered, when the decision was taken to axe that route from the project? Leith Walk itself has been futilely excavated twice already to prepare for the trams that never came. This is clearly not a new concept.

Some of the parameters may have changed, and new information is available - for example the performance of the existing trams and their passenger numbers - but it is still a huge amount to pay for a feasibility study.

Nevertheless, developing the system further appears to be the only way forward, and realism in costing it is vital.

The chastening experience of the trams so far - £300m over the original budget to deliver only two-thirds of what was envisaged when contracts were signed - is evidence of that. An inquiry into how the budget for the existing route spiralled out of control is already underway.

Critics would rightly be unsparing if the council pressed ahead with extending the tram line without due diligence about the likely cost.

Perhaps any calculations should factor in the reputational cost to the city. Edinburgh's image has been hugely damaged by a series of disasters, not all of its own making, from the woes of the Scottish Parliament, to the property repairs controversy and the Mortonhall baby ashes scandal.

Whatever the cost of extending the trams is estimated to be - £80m is suggested - throwing any more public money at the scheme is going to be a hard sell, which is why much is being made of potential private investment.

But if an up-front investment will protect taxpayers in the future, then so be it. Because there is little doubt this project needs to be built.

While passenger numbers on the existing route have been sufficient, they have not been stellar. For many in the city the tram lines as they currently exist will never be of much use, and many feel there are good alternatives even when travelling to the airport.

The long-term viability of Edinburgh's trams depends on more of the original route being built, with the link through to Leith the bare minimum.

So far the network, has cost at least £776m with interest on loans expected to push the total close to £1bn.

In that context, a suggested £80m to significantly increase the usefulness of the trams may be a bullet worth biting.

The trams are already synonymous with the word "costly". The network has to be expanded if the term "white elephant" is not also to be applied.