The improvement converted the road to grade separated two-lane dual carriageway standard. The British Government at the time decided that a motorway standard M56 extension would be too environmentally damaging, and instead opted to utilise part of the existing road while providing off-line bypasses for all of the at-grade junctions.
The upgrade involved transforming the road into a more efficient and safer two-lane dual carriageway with grade separation.  The British government chose to prioritize environmental considerations by using existing roads and building bypasses for at-grade intersections, rather than constructing a new motorway extension.