But surely it should be simple enough to look at what alterations have been made on other lines already and start off from a basis that is at least as good.
The design and planning process for UK infrastructure is already notoriously expensive and we already do significantly more "planning" than we used to do 100 years ago (when we were actually capable of rapidly building high quality infrastructure).
I would expect there to already be consultants doing similar to what you've suggested however the work is complex and many will be quite cut-off from the build process or only around in the short-term.
Sounds like many of these issues could be described with better knowledge sharing and more tightly coupled processes between planning/building/maintenence.
It sounds quite fatalistic what you've said, that we've basically reached maximum planning saturation so we can only pay the costs afterwards when things go wrong.
But surely questioning these assumptions is good for our civic involvement and for the lines.
I agree that it would be fatalistic to not try to improve the situation using technology, I'm just trying to explain what happens as you try to do so with more planning.
while 100 years ago we built rapidly, there was a large cost in human lives. Planning is part of how we solved that - only part of it, but it is a factor.
With a constant rotation of contractors and the government staff overseeing them, offering innovative solutions at a better price than the next bidder, opportunities to learn from experience are difficult to achieve with large multi year projects
Or they decided it was an opportunity to test potential improvements. Testing them on a new line where fixing any "improvements" that don't pan out will be perceived as an improvement might well be better than testing them on an old line where any regressions will be immediately perceived as such...
I would expect there to already be consultants doing similar to what you've suggested however the work is complex and many will be quite cut-off from the build process or only around in the short-term.