OK, so here's another attempt at designing the junction to a) freeflow the two important movements, b) be full access, c) be fairly easy to build without disruption and while taking advantage of the existing bridges; it can even handle D2M! As a bonus, it should be fairly easy to navigate through (it's easier to understand than HE's old plans for the junction, at least). The trade-offs are that some of the connections are lower-speed and some of the minor movements will be slow. Green and red lines (i.e. the A460) are all single-carriageway, and (apart from the roundabouts, obviously) two-way traffic.
The main realisation here is that placing a loop in the southwest of the junction would fix both the vertical alignment problems (the area is very hilly, so it helps to have a good 3D map of the area when planning junction designs), and the issues with the existing bridge being at the wrong angle.
The traffic lights in the south-east are the only way I could fit the existing slip road into the space available, but they should only need two phases and don't affect any major movements. (The curvature of roads shown is to aid driver understanding; drivers coming from the M54 will see a turn-off for the A460 southbound and an "all other routes" "straight ahead", drivers from other directions will only have one option. When going south, the road would be laid out as though the whole thing were a right turn filter lane or even a jughandle, and the green lights would show right arrows, to make it clear that you couldn't go "straight on" onto the M54 in the wrong direction.)
The main concern I have with this design is the merge from the local roads onto the M54 westbound. Because there's a roundabout just out of view to the south, you could move this pretty much anywhere on the map, but any position seems potentially awkward from a merging safety point of view. (The given position seems like the easiest solution to the issues, because you could lay it out as a lane drop + lane gain, meaning that there would be no issues with an immediate merge and giving plenty of time for people to find a lane with a suitable merging distance before reaching the M54 mainline.)
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