Here, on the A449 north of Worcester, the northbound carriageway has been remarked as a single lane. Again, I believe this is for safety reasons; I think the northbound carriageway is the original one, and is thus rather too narrow to safely fit two lanes around this corner (plus a few more later on). The southbound carriageway, by contrast, is two lanes at this point.
I well remember the construction of the northern bit of that section of the A449 (north of Ombersley) in the late 70s.
It appeared well designed and fast, but they left a number of poor junctions with side roads, plus narrow refuges for turning.
I see that has now all been narrowed, and all the refuges have been stopped up meaning long loops to turn right.
It renders the whole scheme rather pointless.
These days I am more familiar with the A541 Wrexham-Mold road past Plas Teg, and that was dualled by adding a straighter carriageway to one side, leaving the original carriageway to weave about, and all at 70mph.
The old side was first singled and reduced to 50mph, and now the new straight side has been reduced to 50mph too.
There are also a large number of originally fast 3-lane roads in the area (1950s trunk road single carriageway design with a middle lane) which have become 2-lane to avoid head-on crashes while overtaking.
If you are lucky there might be double-white lines for a spell to overtake, but mostly you just have to stick in line.