the amount of congestion on the motorways at the turn of the century meant something had to be done. widening schemes were (are) very expensive so other solutions had to be tried first (and seen to fail) before any road widening would be authorised. the concept of the managed motorway was born.
the M42 was the first, and it worked - journey times became 27% more reliable.
https://www.roadtraffic-technology.com/projects/m42/
as with everything then interfered with by civil servants though, the M42 solution was declared "over engineered", and subsequent schemes were done on the cheap - distances between refuges increased from 500-800m to a mile and a half, number of cameras reduced, number of gantry signs reduced, etc.
it could have worked everywhere if the highways agency had been allowed to make the scheme specifications match the risk assessments done for the M42 scheme. but money talks.