The Government's formula for "spend" on road improvements allows for 44p per minute saved per car driver through a notional 60 years of the life of the road, according to a recent article in New Stateman. The figure is rather less for bus passengers and cyclists - 33p and 28p per mile.

http://www.newstatesman.com/200708090012

What would it mean is a similar pattern was applied to the "TransWilts?". I'll forcast a saving of 30 minutes per journey on 100,000 journeys next year, rising to a saving on 2 million journeys in 20 years time (I can justify that - it's based on an 8% compound growth which is way below what was historically achieved, and comments elsewhre confirm that there's no ceiling to growth at least in the next few years).  And I'll value rail passengers at a miserable 30p per mile, giving an investable amount of 9 pounds per journey for 23 million journeys.

So if it were a road, the TransWilts would be eligible for investment of 207 million pounds to cover just the next 20 years ....

[i]For anyone who feels so inclined to check my figures, here's the program code written in Python that I used to count the journeys.