[OSM-talk-be] bridge or tunnel?

Tue May 28 21:56:17 UTC 2019

 Hi,

First: the interpretations given here to 'tunnel' are much more strict than the wiki, which leaves much more room for interpretation. A strict interpretation of tunnel makes the use of tunnel=yes of tunnel=culvert for passages of rivers underneath a road senseless, just as tunnel=building_passage.

Second, I hope that you are aware of the consequences of your interpretations. Let's use the definition of Marc, which is the most elaborated: "I apply the rule: stand on the road, look up, which layers of material do you "see" before you reach the sky? Is there earth (grond/aarde) that was not placed there artificially, then you are in a tunnel.": Then the 'railroad tunnel' between Brussels North and Brussels South is NOT a tunnel. It is just a mole pipe (in the words of Gerard). The whole thing is dug out, built and then covered with streets, buildings and here there a bit of gorund.
Even a lot of the metrotunnels are made with the 'cut and cover' technique and are thus NO tunnels? Ecoduct Kikbeekbron over the E314 is NOT a tunnel?
Also the examples given by Marc and Tim with such a thin cover are most likely made 'cut and cover' and have only 'artificial' things overneath: NO tunnels...And what do you do with the GEN-constructions at railway 161 in Genval? The railway has been covered with roads and parking lots. Also no tunnels? 
On the other hand: ecoduct Groenendaal really looks like a bridge but has been mapped as a tunnel...

Lionel said : "A tunnel is generally something that was dig (removing earth/material) and consolidated from the inside (most often with concrete) like a subway tunnel if you want. It seems pretty rare to dig a big hole, make a tunnel and put back the earth on top !": Yet, that ís a very common practice...

So to me these seem to be useless definitions...

Or does the word 'artificial' means that ground level matters? The ringway around Antwerp (R1) is almost everywhere at level -1, below ground level. The cutting is here the artificial structure (using Yves' words this time). So where there is a road going overneath, the ringway goes through a tunnel...? The same for Joost's example: if you look at the aerial imagery, you can see clearly they had to dig out the N28 to get underneath the railway and the other roads: thus a tunnel...? And what about the complex traffic changers where it is often very hard to see what the original ground level was.

@ Yves: 'Layer' gives a relative position. Something at ground level can perfectly have layer=-1 or layer=1. Check the wiki. And further: a bridge with layer = 1 doesn't mean it is above ground level; a tunnel with layer = -1 doesn't mean it is below ground level.

@ Tim: What came first is a useless criterion. The E313 was constructed before the E314, but it is definitely a bridge of the E313 above the E314. And the definitions of bridge or a tunnel should be so that anyone knows whether to map things as bridge or tunnel without having to know in which order roads, railways, etc. were constructed.

So can someone can come up with a useful definition?

Can I come up with a definition? I like the length/width ratio, the open bridge(like) structure against a confined tunnel(like) structure. And the fuzziness of the wiki. But one thing is very clear for me: ground level doesn't matter. 
Regards,
StijnRR

    Op dinsdag 28 mei 2019 18:52:50 CEST schreef Marc Gemis <marc.gemis at gmail.com>:  

 This is the place:
https://www.google.com/maps/@51.2216551,4.0345363,3a,75y,49.39h,77.96t/data=!3m6!1e1!3m4!1sjggCIzrpgLhVFtrn6gYCnQ!2e0!7i13312!8i6656
(sorry no Mapillary images yet).

Burchtakker (the parallel road) is lowered near the (bicycle) tunnel
under the E34/A11.

On Tue, May 28, 2019 at 6:36 PM Marc Gemis <marc.gemis at gmail.com> wrote:
>
> I think there is a tunnel under  the e34 between Antwerpen en Zelzate.  There used to be a level crossing which was removed and instead they created an underground passage for it.
>
> M
>
> Op di 28 mei 2019 14:46 schreef Lionel Giard <lionel.giard at gmail.com>:
>>
>> @joost schouppe  To me that's indeed a bridge, as you see the same structure as on the motorway bridges : a platform supported by pillars....
>>
>> A tunnel is generally something that was dig (removing earth/material) and consolidated from the inside (most often with concrete) like a subway tunnel if you want. It seems pretty rare to dig a big hole, make a tunnel and put back the earth on top ! ;-)
>>
>> I can't find example of tunnels that's really like "under a railway or motorway", so i would say that probably 99% of the tunnel are below ground or mountains/hills (if we exclude the obvious building passage that we classify as tunnel in OSM). They are generally longer than wide as someone quoted from wikipedia.
>>
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