Borders railway - £300m for about 30 miles of new railway connecting a number of small towns to Edinburgh. Good value? If you had £300M to spend on any other railway project which would it be, why that one and why would it better value for money than the borders railway? Don't answer for projects that would would probably cost more.
I think the thing which tends to confuse people about Borders Rail is that it is essentially 2 different railways.
There has always been an excellent Business Case for opening an Edinburgh commuter line to Midlothian. This has very similar characteristics to many Scottish reopenings of the last 30 years from Bathgate and Paisley Canal in the 80s, to Alloa and Larkhall in more recent years.
A service connecting Glasgow / Edinburgh to currently non rail served commuter belt towns on their outskirts has been shown to work time and again.
However where Borders Rail went beyond this tried and tested pattern was to extend a little further beyond the existing commuter belt to reconnect a more distant area to a new labour market. This kind of reopening is not captured well by existing business case methodology as it is about changing travel and commuting patterns, new house building plans and inward investment changes. Not to mention more ephemeral benefits like the economic benefit for the central Borders of being "On the Map".
The fragility of this business case was recognised by early promoters and the Bill Committee at the Scottish Parliament inserted a handcuff clause forcing the completion of the whole route to stop it being cut back to the better business cased Midlothian section.
There has always been an explicit recognition that the Borders element of the scheme was political, initially as a Lib Dem concession for joining the 2003 coalition, then as a symbol of SNP commitment to traditionally less fertile nationalist territory of the Borders.
If you wanted a stronger traditional business case return for a similar amount of money then you could probably have put it into three £100m schemes with more traditional commuter benefits (Midlothian, Levenmouth and Penicuik rail lines say).
However until we see the economic effect a few years down the line it's impossible to judge whether this would actually have have generated more benefits, as the expecting outcomes from Borders Rail are both longer term and more difficult to quantify than a traditional reopening.
In the short - medium term though I'd expect the scheme to wash it's face very nicely through fast growth on the Midlothian section.
The best comparator in this regard is Airdrie - Bathgate. This line has seen very strong growth at each end from Glasgow to Airdrie and Drumgelloch and from Edinburgh to Uphall, Livingston North, Bathgate and Armadale.
The volume of traffic over the middle section has taken longer to build up as it involves changing travel and economic patterns that have taken 50 years to form and it is only as people move house/job or move into new housing areas that these travel patterns change.
It is undeniable though that the service has helped drive economic growth in these areas. I strongly suspect Borders Rail will do the same but judge it in 10 years time not in 12 months.
