What happened in the past when the railways were dominant?
In the past there were many more diversionary routes available...
I also suspect that a great deal of engineering work was carried out in a more dangerous way - with neighbouring tracks still open, and even between the passage of trains. This sort of thing wouldn't happen these days:
The Board of Trade report, published on 21 June 1865, found that for the previous eight to ten weeks a team of eight men and a foreman had been renewing the timbers under the track on viaducts between Headcorn and Staplehurst railway stations. The track would be removed when no train was due. However, on 9 June the foreman, John Benge, had misread his timetable as to the schedule that day of the tidal boat train, which ran at a different time depending on the tide in the English Channel.
From
https://en.wikipedia.org/wiki/Staplehurst_rail_crashWhen I started on the
S&T▸ way back in 1969 on the Southern end of the four-track West Coast Main Line, engineering work was always carried out on two tracks, with the other two open for normal use. No blue fences in those days either.....**
The only time we did full closures was for major track/signalling alterations and if I remember correctly those used RT Double Decker buses from LT.
Edit to add: ** and Yes, I know times are different now.....