When does a tunnel need to have a man_made=bridge on top?

How you decide?
I guess size has something to do with it. Does it matter what can go under? Bikes, cars, boats?

I would say you can map man_made=bridge whenever there is a bridge structure, if you want to specifically map the physical structure (i.e. going beyond indicating that a way passes over a bridge).

Iâ€™m not sure how this relates to tunnels though. E.g. if one road passes through a tunnel (through earth, rock etc.), and another road passes over it on the surface, the latter is just a â€śnormalâ€ť road with no bridge structure. Are you thinking of a different situation?

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Technically, it does not. Either the road below is a tunnel or the road above is a bridge (well, if thereâ€™s a third way on ground, there can be both a tunnel and a bridge). I generally use a rule of thumb (exepct for proper galleries like this one): if the road below is under the earth level is a tunnel and the road above is a standard road; if the road above is over the earth level then itâ€™s a bridge and the road below is a standard road. This is my personal way of mapping, but I donâ€™t think thereâ€™s a general rule on this. Itâ€™s up to the mapper belief.

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+1

This does not always work, sometimes you can have bridge within excavation below local earth level.

Personally I look for presence of earth/rock above passage (if there is rock/earth above discussed passage then it is tunnel, if only constructed deck - then bridge)

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This itâ€™s even better. So in a case like this you would tag the above road with bridge, right?

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Ignore the word tunnel, i meant just a passage underneath.

Classic tunnel is easy to spot when it long. Sort of the â€ślight in the end of the tunnelâ€ť.

Here is few photos its not so clear if the structure is a tunnel or is it a bridge above:

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Iâ€™m not sure if thereâ€™s specific tag for such passages, but I guess tunnel would make more sense in this case, as itâ€™s below earth - type of ground.

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In all of these cases the road is for me the ground level. All the animal crossings are bridges, except for nr. 8, where it is a tunnel.

The road does not elevate and the structures look like they are build over it. This means for me, they are bridges. This might be different for tunnels through mountains, where there is no elevation either. But I think it always depends a bit on a personal view.

From a constructions companies pov these are all bridges except of no. 8 (agreed with @Robert46798). We had a similar topic recently in the german forum and there was some kind of a consensus to tag the main structure as man_made=bridge + layer=1 and on top man_made=wildlife_crossing + layer=2 + natural=srub/grass or whatever is applicable. Additionally fences, noise barrier walls and tracks (which sometimes exist implemented in the wildlife crossing) as far as applicable. Example:

Way: â€ŞGrĂĽnbrĂĽcke Teupitz/Tornowâ€¬ (â€Ş242850373â€¬) | OpenStreetMap

One may argue in case 2 and 7 the street is located in a cutting - this is not ground level.

Yeah, on a second look I realized this too. But from the appearance this is a bridge over a street. - And now the differentiation becomes very vague, what was the origin of the post

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I remember an example of a tunnel on a bridge, just one road (crossing water)

yes, and the lower road as cutting.

A tunnel is dug into the ground (always tunnel), or sometimes it is constructed openly and covered afterwards, there are (different AFAIK) criteria to determine whether these count as tunnels in specific jurisdictions, you would have to ask a civil engineer about it, and there will be precise definitions.

For osm, I do it like this: if there is a bridge structure above, it is a bridge and not a tunnel, if it is dug it is a tunnel, if it is closed after construction but quite long it is also a tunnel

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yes, for me it looks like bridge - and 10 upeaa siltaa, jotka on tarkoitettu vain elĂ¤imille seems quite clear case of tunnels (maybe except one with elephants)

Why it would be relevant? What about round going in tunnel though 30m high embankment - would you also mark it as a bridge because road is at ground level?

Is it really supposed to be a bridge: https://www.railadvent.co.uk/2022/06/watch-timelapse-footage-shows-a-railway-subway-being-built-in-sussex.html ?

It is at ground level.

In my opinion it is a tunnel.

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It was just my first approach to differentiate those two. To get a better understanding I looked to Wikipedia:

A tunnel is an underground passageway, dug through surrounding soil, earth or rock, and enclosed except for the entrance and exit, commonly at each end.

So look for the ground level to whether something is underground sound reasonable to me
On the other hand you provided a fine example with the embankment, where the way goes through soil, although it is on ground level. As it is also mentioned as tunnel in the article it seems feasible to see it as tunnel.
tunnel=building_passage is also an example where the ground-level-approach does not work.

Therefore: If the way goes through soil, earth, rock it is likely to be a tunnel.

Remaining with the provided Examples: Especially picture 5 is hard to categorize for me. Still it looks more as if the structure is build over the street, so therefore it would be a bridge for me. But this may influenced by my language/experience, as in Germany this would be called a wildlife bridge

Considering the said:
I would ask for a specific way whether it was build to get through a structure (ground, building, embarkment, â€¦) =tunnel, or to get over it =bridge. In this case the length or transport mode would not be relevant.

The embankment case make me the most uneasy with classification. My gut instinct is to ask â€śdoes it look like itâ€™s supporting soil which itself supports other things or does it look like it support the road/footway directly?â€ť. If the former I would tend to say tunnel even through an embankment (with some nervousness), the latter a bridge even if in over a cutting.

Even this approach has its difficulties, many traditional stone bridges look a bit like tunnels through fill even though they are definitely bridges. I suppose they get too thin at the top but with barriers at the sides thatâ€™s not easy to see at â€śriver levelâ€ť.

The wildlife bridges are an odd case as they are clearly thought of as bridges even though some look like tunnels through embankments to me.

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Funfact: in the GDF (a navigation data format) they use the class brunnel (Bridge or Tunnel) to avoid these discussions.

For tall truck, or large transport, it matters a lot. Unless you want to break your vehicle.