One technicality to mention though is that once an onslip itself no longer has physical separation but forms part of one continuous road surface of the main parallel dual route then it can be considered 70 mph, generally parallel enough by that point too to meet the legal definition.

I'm not sure they can be called expressways either, since cyclists, pedestrians and even horses are permitted.

This wasn't a correction, but a degradation in OSM data quality. If you contact Department of Transport, or any Speed Awareness Course leader you’ll be told that dual carriageway (not motorway) on/off-slips in the UK are treated as a single road just like any other single carriageway, and so in law remain 60 mph for safety blending with main expressway traffic. Commonly broken law, admittedly.

Please give this a read:
https://www.whnsolicitors.co.uk/newsroom/individuals/private-road-laws-uk/

It seems Southampton council don’t have a good understanding of common law, or they have curious by-laws for their particular jurisdiction. It has affected your judgement. Never assume councils know what they are talking about, or that their data is up-to-date or complete for that matter.

Roads can be adopted, or unadopted, and at the same time either publicly or privately-owned.

In this case from NSG:
USRN: 4600057
ABELS CLOSE, FELTHORPE
Classification: Neither M, A, B or C
Responsibility: Not maintainable at public expense, Private Street Manager.

You also appear to reject the existing wiki article specifically mentioning 'for residents only' access being treated the same as access=private.

Yet you reject access=destination, access=permissive on a basis of being uncertain yourself. Also, is this not a discussion itself, which you already publicly highlighted for others to comment on?

I have yet to get any rational justification for your strange view. How would you handle an unlocked gate for example, on private land, signed private? Granted there are those who need access in that case such as delivery agents. Ordinary public taking photo on said ground? I think not.

There have even been cases of thin 'ransom strips' of land being privately acquired in order to prevent access over otherwise public or accessible highway. There doesn't even need a sign to be there, just that the land itself be privately owned. Much like I wouldn't tolerate you on my home patch of private land.

It is clearly private because of the signage stating it is private or "for residents only". The land at supermarkets is private too but with customer permission while opening, gates and secured facility after locking up. Why are you struggling with this?

Your lack of understanding of private roads. Seriously, go search for 'uk what makes a road private' in your favourite AI search utility. Private roads don't necessarily need to display a 'private' sign, but they ideally should. Under your definition you would be happy to trespass on private land. In the UK, a road is private if it’s not on the highway authority’s list of roads they maintain, or if it’s unadopted. The NSG here states: USRN: 4600057
ABELS CLOSE, FELTHORPE
Classification: Neither M, A, B or C
Responsibility: Not maintainable at public expense, Private Street Manager, Street State: Open.

So a private landowner can have a road they maintain, a private sign, but it’s not actually private unless they erect some form of physical barrier? The private-signed road outside my house, where certain residents who zoom down here get very tetchy towards geriatric dog walkers attempting to make use of it.

Of out of curiosity, when would you tag a road as access=private?

Don't you think that same convenience and simplicity should apply to the data users of OpenStreetMap? There’s a reason these highways are mapped as separate ways. Just wish the council's system had it like that too. They often only just deal with simple junction geometry.

I could just about accept highway=trunk_link for the straight-ahead per green arrow LED traffic lights here, since eastbound connects with highway=service.

You seem a bit confused. Adopted status is purely whether the highways authority maintains the road. Public highway has to be declared by the same government body and be in public ownership. Neither is the case here. Abels Close is not in the council’s list of streets, nor in their GIS.

A road once divided by a physical barrier is legally no longer a single road, by the way, but two or more. The on-the-ground eastbound signage shows the left/through lanes with white background fill and the right-turn lane with green for primary.

An unadopted, private road is not a public right of way, unless it is defined by the definitive statements (can be hinted at from the definitive map) as maintained by the county council. There is clearly an access rights case to indicate that this is not access=yes.

From a driver point of view on the Ring Road, however, now there's a sense of ambiguity where before there was clarity. Are you local to the area?

Sainsbury’s I’m sure would be proud that they have a trunk road direct to their store.

(I note you ignored my advice about discussion before deleting)

There’s literally a sign on this private road saying access is for 'residents only'. Does that sound like a public road to you? No physical barrier of course, but does not meet the third rule of the HCR case judge to permit a traffic order.

If you don't like access=private, how about access=residents?