Marking a PROW as a bad idea

The wiki documents:

Tagging can be applied to the intersection node or the location of the signage

so tagging the location of the sign is OK. But the wiki does also document that it should be accompanied with traffic_sign=hazard to show it’s the sign, rather than than the junction that is being mapped.

Technically, no it isn’t. It’s just warning of a side road:

The yellow backing actually doesn’t convey any additional “warning”. Local authorities are free to add the fluorescent yellow backing however they chose.

You’re free to add a dangerous junction warning if it is indeed a dangerous junction. Which you seem to be able to verify that it is. But it’s probably wrong to tag the sign as such, since that isn’t what is being conveyed by that sign.

“Technically, no it isn’t. It’s just warning of a side road:”

Why do you think that the side road is being warned about then? What justifies a warning sign about a junction being there? After all it’s hardly a standard thing for all junctions. To quote from the Traffic Signs Manual, chapter 4:

“Warning signs are used to alert drivers to potential danger ahead. They indicate a need for special caution by road users and may require a reduction in speed or some other manoeuvre.”

“Junction warning signs should be used sparingly where there is a justification. They are not normally provided on very minor rural roads, nor in urban areas where road users can expect to encounter junctions and signing every junction is both impracticable and increases clutter. They may of course be used where a specific need has been identified.”

The reason that they are used sparingly is that they are only used where the junction is more dangerous than usual and directional signing is not provided. It can be more dangerous because the side road is not obvious. It can be more dangerous because the side road is particularly busy. It can be more dangerous because the side road has particularly limited visibility for those emerging.

So they very much are warnings for dangerous junctions.

As for the yellow surround? That’s simply to make the sign more visible to those on the main road, hence the emphasis I referred to. Oh and local authorities are NOT “free to add the fluorescent yellow backing however they chose (sic)”. To quote from the Traffic Signs Manual chapter 1:

“Yellow backing boards are intrusive; they should be used sparingly, and not as a matter of course. They can reduce the attention drivers give to other, more important, signs and over use could eventually devalue their attention-attracting benefits.”

Further in chapter 4:

“Where it seems that a sign is not being noticed by drivers, it should be checked to ensure that it is well‑sited, not obscured by foliage or other obstructions, and is of the appropriate size and in good condition. Only then should the use of a yellow backing board be considered. They should be used very sparingly and not as a matter of course.”

So they very much are warnings for dangerous junctions.

I’m 100% not a traffic sign expert here but the definition of sign 505.1 is to warn of the presence of a junction and inform of priority. Beyond that (i.e. adding the word “dangerous”) is open to interpretation. In the text you link to, there is no mention of the words “dangerous” or “hazardous”, only about “justification”.

I remain unconvinced that every side road warning sign justifies a hazard=dangerous_junction tag in OSM. Indeed, the Wiki even seems to suggest this is a tagging mistake. ETA: But maybe others disagree and think we should, so who knows?

I do, of course, agree that triangular road signs warn users of hazards. But something like hazard=side_road might be more appropriate.

I have also said if you can confirm this is a dangerous junction, then there is no problem tagging it as such. But the presence of this sign alone doesn’t seem to warrant it.

Oh and local authorities are NOT “free to add the fluorescent yellow backing however they chose (sic)”. To quote from the Traffic Signs Manual chapter 1:

I was being a little tongue in cheek. But the point is, (as far as I know!) there is no legal criteria of when yellow backing must or must not be used. It therefore comes down to the decision of local authorities, and some seem to have very different criteria about when they are and aren’t used.

As you even quoted, it doesn’t necessarily indicate that the junction is more dangerous than a non-yellow backed sign. It could just be that this sign otherwise isn’t likely to be noticed by drivers.

Did you see this by the way? I would recommend you update the tagging of that sign so that it is correctly mapped as being a sign, avoiding any confusion about this being a junction.