[Tagging] Feature Proposal - RFC - More Consistency in Railway Tagging

[Martin Atkins]

On 04/13/2013 04:21 AM, Kytömaa Lauri wrote:
> Martin Atkins wrote:
>
>> Refine the basic railway=* tagging to have a more specific definition,
>> taking inspiration from the tagging conventions around highway=* .
>
> IMO this is flawed in two ways:
> - on empty highways, one can drive in circles on the whole road surface (not that one may or should, but they can). For anything that moves on tracks, the switches are the only place one can change course. This makes the individual tracks and their connectivity "the network", that is the roads they happen to run on are not the network itself. Drawing a single way where there are multiple tracks is not wrong, but it's just an intermediary solution before somebody has the time to add the switches and separate the tracks.

While this is true from the perspective of the railway operator, I would 
argue that passengers of the railway perceive it a single "road" where 
they travel in terms of the route relations placed on top of it, not in 
terms of the physical track layout. When I ride on a railway, I don't 
care about where the switches are, I just care about whether the train 
will stop at the two stations I'm interested in (in the correct order!) 
and whether the route it's going to take is a sensible one in terms of 
distance.

I agree that the next level of detail can be mapped too, but I don't 
agree that level of detail is interesting for the common cases of 
routing that schematic mapping is aimed at, for members of the public. 
Therefore it should be handled via a separate set of tags, just as 
highway tagging has a progression of tagging detail from the basic ways, 
to the individual lanes, to the actual area occupied by the roadways, 
with each "layer" complementing the previous rather than conflicting 
with it.

> and more importantly
> - there are an abundance of places where the tracks switch from the simplest case "in the road" to short (or long) bits where a separate way is required ; that is, for example where the tracks diverge from the lanes and a stop platform is between the tracks and the lanes for other motorized traffic.  Were the adjoining simple case ways just one tag on the road, you 
would introduce arbitrary(!) turns and kinks in the course of the tracks.

Someone (you?) noted this on the talk page too, and I updated that 
example to talk about the platform, but I'm not sure this example is 
specifically about railways... even if the railway weren't there and the 
platform were for boarding a bus (a situation which also occurs in San 
Francisco) it would still be necessary to split the highway if one 
wished to show the platform location; if we were to just draw the 
platform next to the separated tramway without splitting the highway, it 
would be unclear that the platform is within the roadway at all, just as 
it would be unclear whether the tramway is in the roadway.

 > Other variations exist, too. There's an example of such kink in your 
proposal's example photos, the one where the two tracks suddenly come 
together when they go into a tunnel.

Assuming you're talking about the rendering example I showed [1], I 
considered that case an example of two mappers with different opinions 
about how railways should be mapped, rather than a necessary kink in the 
railway; I was using it to illustrate the idea that the lack of detailed 
guidance on how to tag railways has caused differing approaches in 
different places.

> Tracks shown "outside" the highway where they are not, is just a rendering issue in one map, at extreme zoom levels.

Rendering is just one symptom of the inconsistency between railways and 
highways. Another symptom is that e.g. level crossings get tagged twice 
-- once for each track -- even though they operate as one autonomous 
unit that only risks stopping the traffic once. This can have an impact 
on automobile routing.

> There's already tram:lanes=yes| etc. as an additional attribute tag on the highway way to say "the lanes of this highway contain tram tracks, which may well be drawn separately".
>

I was only able to find what you described on a proposal page on the 
wiki[1], but in the following form that seems compatible with my proposal:

railway:lanes=|tram|tram
direction:lanes:forward=backward|backward|forward
direction:tram:lanes:forward=|both_ways|both_ways|


[1] http://wiki.openstreetmap.org/wiki/File:Doublewaytram.png
[2] 
http://wiki.openstreetmap.org/wiki/Proposed_features/lanes_General_Extension/ProposalPreVoting