What is the pupose of these signs?

When I first saw them I thought they were a mistake. When they remained I thought it an overlooked aberration, but now they've been up for months now and I have to ask why?

I'm talking about the four (yep four) road narrow signs on the Minster Road dual-carriageway travelling from Kidderminster.

I'm travelling in lane 1 of the dual carriageway and approach the tip. The road gains an extra left-hand lane to act as a slip into and out of the site and is then removed a bit further on. During this travel period I have remained in lane 1 following it around the slight diversion where the road expands and contracts. Note that both lane 1 and lane 2 are present at all times until the end of the dual-carriageway further up.

Now put four signs up (two each side) before the tip warning drivers that the road narrows on the left and what are you supposed to think? I'm in the first lane of two and I see a sign telling me that the lane I'm in is merging to the right. Logically I switch lanes drive past the tip and the road expansion and then get back into the lane that never closed.

Seriously I've watched obvious non-locals reach the signs and change into the right-hand lane before finding that past the tip they're expected to turn right in this lane when they want to go straight and then have to pull back into the lane that they had no requirement to leave.

So any officials reading this - what is the purpose of these signs?