Hello Siberiano,

I think the tagging where tram rails are exactly located, is not perfect. Some time ago there was a discussion on the openrailwaymap mailing list: http://lists.openrailwaymap.org/pipermail/openrailwaymap/2016-November/000550.html. It was about the tag for surface vs. embedded. The wiki page in EN uses “embedded”, that in DE uses “surface”: http://wiki.openstreetmap.org/wiki/OpenRailwayMap/Tagging#Tracks, http://wiki.openstreetmap.org/wiki/DE:OpenRailwayMap/Tagging#Gleis.
Maybe it is worth to start a discussion there?

However that doesn’t say enough about the location of the tram rails in the street area. The cases 3, 4, 5, 6 should be clear in so far as the street has separate ways for each direction and the tram is in between. Here in my city (München) this area is then mapped with landuse=grass, if it is covered with grass. I think for a few tracks I added surface=grass. If it is not grass, landuse=railway might be useful. A barrier could be mapped as a line with barrier=fence.
More complicated are those like your case 2. Is it still a lane of the street or a separate area? The traficability might be intended to be used for ambulance or the fire brigade, but it could be also a shared lane tram/bus and bus lanes are normally part of the street.
This https://www.openstreetmap.org/way/49863567 is such a bus way with one lane for each direction, formerly used by tram also. It is separated by kerbs from the street.

If you want make an analysis, how many tram lines are separated, I think that will not be possible from one particular tag of the railway=tram with the existing tagging scheme.

Bye,
Rainer