Lincoln avoiding line (Known as the 'The High Line' locally) closed 1983.
And still sorely missed. Built as part of the GN/GE "Joint" line, from Greetwell Junction to Pyewipe Junction and bridging Canwick Road, the High Street, and Beever Street thereby avoiding the problems caused by the three City Centre level crossings on the original GN route (Durham Ox, High Street, Brayford). In particular it allowed freight trains to run on the route whose length exceeded the distance between the two crossings (as it was not permitted to have both crossings closed to road traffic at once, because of the risk of a stalled train cutting the city in two.
There was a triangular junction at the west (Boultham) end of the avoiding line to allow trains from the east access to the large freight yard there. This survives, as it was re-used for the spur connecting the Newark route to Central station, opened in 1985, but that actually increased passenger rail traffic across the High Street (as the Newark trains used to terminate at St Marks, west of the High Street), as well as requiring all freight traffic to do so.
Following the construction of four bridges east and west of the city centre, (the first in 1958 and the most recent just ten days ago), the High Street is now closed to road traffic at the level crossing - severing a highway that dates from Roman times.
I did once travel on the avoiding line, in about 1970, on a special charter to Liverpool Street, for my school in Lincoln and one from Market Rasen, which, to avoid reversal in Lincoln, used the avoiding line to access the "Joint" line to March.
Sunday ECML diversions over the Joint line tended to run through Central station even if they were not booked to call, as the line was "switched out" on Sundays. However, it was a common sight at Lincoln City home games to see trains rumbling past.
With the increase in rail freight traffic over the Joint Line re-opening it would be a good move, but sadly a short-sighted city council has allowed most of the embankments to be removed and houses built on the land.