Of all the extravagant schemes devised during the Celtic Tiger era to squander public money, two of the most spendthrift must surely have been the proposed underground rail lines for Dublin.
These were Metro North, from St Stephen's Green to the airport and Swords, and the Dart Underground from Inchicore under the south city centre to Spencer Dock.
Metro North, which was supposed to cost €3.3bn, is already dead in the water. It will almost certainly be junked in favour of a far more modest spur running from the existing Dart line to Dublin Airport that will cost 'only' €790m.
Will Dart Underground be next for the chop? Taxpayers should definitely hope so. If Metro North was extravagant, then Dart Underground must surely count as extravagance squared.
After all, it called for the digging of a tunnel under the south city centre at an estimated cost of €4bn.
There are concerns that Dart Underground cannot be delivered for anything close to €4bn.
Let's look at the two main tunnelling techniques.
There is cut and cover, a relatively cheap method, where a trench is dug and the tunnel is dropped into the trench that is then covered over. Unfortunately, that's not an option in a densely built-up area such as Dublin's city centre.
This only leaves the far more expensive method of tunnel mining, where a tunnel is laboriously dug beneath the city streets.
That a 7.6 kilometre tunnel could be constructed by this method for €4bn, a cost of just over €500m per kilometre, is arguably optimistic.
After procrastinating on this issue for more than four years, it finally looks as if the Government will soon have to make a decision about Dart Underground.
A 2014 High Court decision set a September 24, 2015 deadline for the issue of the notices to acquire the properties needed to construct Dart Underground.
Will the Government give the go-ahead for the issue of these notices or will it abandon the project?
Well, as was the case with Metro North there exists a far cheaper alternative to Dart Underground. In fact, there are two alternatives.
As many older railway travellers already know a railway connection between Heuston and Connolly Station already exists.
Instead of proceeding with Dart Underground, which would be tantamount to pouring money into the ground, this tunnel should be used as a stopgap solution to connecting Dublin's two main railway stations.
A longer-term solution would be to construct a tunnel under the Liffey between Heuston and Connolly.
Not alone would such a tunnel be much shorter than Dart Underground, less than five kilometres, it would also be far cheaper, as it could be constructed using the cut-and-cover method.
As is the case with Metro North's likely spur from the Dart line to Dublin Airport, reopening the existing link between Heuston and Connolly and/or building a cut-and-cover tunnel under the Liffey offers a far cheaper solution to Dublin's public transport problems than the grandiose project proposed during the Celtic Tiger era.
If the past seven years have taught us anything it is surely that, if we are going to spend large sums of money on major infrastructure projects, then we have to ensure that we get value for our investment.
We need to devise projects that are cost-effective and can be delivered quickly.
The Dart spur to Dublin Airport, along with reopening the existing Heuston-Connolly line and/or a tunnel under the Liffey are examples of projects that can quickly make a difference to Dublin's hard-pressed commuters.
By contrast, Metro North and Dart Underground will take decades to complete and may end up costing multiples of their original budgets.
Dublin's commuters can't afford to wait.
The Government should pull the plug on both Metro North and Dart Underground and give the go-ahead to cheaper and quicker alternatives instead.