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HS2 is a good example.
In the 1990's there was a proposal to resurrect the 'Grand Central Railway',
broadly Sheffield to London Marylebone, ignoring the fact that the previous trackway had been converted to roads in some places, (Chesterfield?), and huge viaducts, (Brackley?), had been demolished.
This proposal failed, but some bright spark realised that functionality was insufficient to enthuse. They recruited, amongst others, Lord Adonis, and employed only lobbyists.
It was transformed into HS2, but not just a fast train line, but THE fastest train line in the UK, ignoring the practicality of the InterCity 125s that had served the GWR from 1976 onwards.
After the lobbyists, it was economists with a smokescreen of potential benefits.
By then it was unstoppable, and now we have an open ended commitment to build an out of date transportation system 10 years, (and counting) too late.
In my own head (no science) I've come up with a number between 50 and 100 in this group...