It turns out that the huge flat-topped pyramid of hard core and the slightly smaller flat-topped pyramid of earth were actually just the raw materials for a road widening scheme. Why it took them nearly twelve months between dumping the heaps and actually starting work, I don't know. It's quite a major undertaking as it involves a new bridge across a river. It should, however, remove a nasty dangerous bend where there have been many accidents over the years. The downside is that for the past several weeks I've had to negotiate ever-varying configurations of the roadway, governed by hundreds of traffic cones and a set of traffic lights.
There are in fact lots of temporary lights on my route at the moment. My daily drive of around an hour (40 miles) takes me through exactly one set of permanent traffic lights (at the juction between the A494 and the A5)[*]. There are also two Pelican crossings in Bala. But at the moment, there are about half a dozen sets of lights round the various road works that are underway at the moment. This set is the final one just outside Dolgellau, snapped on Friday on my way home from work.
I just wish they'd finish whatever it is they're doing and let me have a clear run!
[*] There is another set at the point where my route leaves the A5 to follow the A494 (the two roads become one for about a mile then part again), but as there's a slip lane for traffic turning left, I don't actually have to take any notice of those lights and merely have to watch that I don't crash into any traffic turning right.