What does this road sign mean? I regularly pass a (UK) road sign that I don't recognise.



My gut instinct is that it's warning me about a bridge or a tunnel but it's on a normal dual-carriageway and there are no obvious overhead structures for more than a mile, nor are there any side turnings that it seems to relate to.

So what the heck is it and what am I supposed to be looking out for?
The 'arch' is actually an arrow - look at the right hand end.

I believe it means there is a junction between the carriageways that allows you to make a right turn and travel along the opposite side.



There's another sign on the other side of the carriageway, and a corresponding u-turn junction.