[OSM-talk] lanes

[graham]

Gervase Markham wrote:
> LeedsTracker wrote:
>> As Shaun says, the unresolved issue of lane handed-ness seems to be
>> blocking this lane issue.
> 
> This is anothe occasion where a generic :left/:right proposal would be
> useful...
> 

I had missed that thread till now. But it doesn't seem to have come to 
any usable conclusion.

I have two problems with the left/right solution (neither original):

- Say I have a bus lane (or cycle lane) running along one side of a 
two-way road (the most common situation where I am).   Just attaching a 
'left' tag to it makes it dependent on nobody ever reversing the 
arbitrary direction attached to the way. I quite often find I'm 
reversing sections of bidirectional ways (eg to join two of them); if 
anyone ever did that with a way with 'lane:left' style tags the lane 
would suddenly flip to the wrong side of the road.

- More serious, I think: it just feels quite arbitrary as a solution: I 
would have to tag a lane as being 'left' in relation to the random 
direction the arrows on the way happen to be pointing, rather than in 
relation to anything in the real world.

Unfortunately the only suggestions I can come up with are pretty lame, 
but maybe they might trigger better ideas in someone else:

1. draw ways as multiple parallel lanes. Maybe all two-way roads should 
be represented as two parallel ways in opposite directions? I'm sure 
everyone would love the work involved in that ;-).

2. have an 'origin' tag to be used on the first node of a way 
independent of direction; if the way direction flipped, the origin would 
stay in place. 'Left' or 'right' would be in relation to the origin 
node. Still completely arbitrary where the origin goes, and how do you 
find it on a long way?

3. Make more of a separation between internal representation of ways and 
user views in josm/potlatch. All ways have a direction which is 
independent of the 'arrowed' direction which can be displayed to users, 
and is fixed - a totally arbitrary value used only as a fixed reference. 
Consider all bidirectional ways 'as if' they were two ways orientated in 
reference to the hidden direction. When a user selects 'add a lane to a 
way' (or bus-stop or any other 'sided' feature) josm/potlatch switch to 
a two-way representation of the way; the user clicks on the particular 
one of the two he/she wants to add the lane to. Internally this could be 
named 'left' or 'right' lane; but the user would never see the words 
'left' or 'right' or need to explicitly tag the sidedness of the lane.
Dumps all the work onto developers and makes it hard for end-users to 
fix things that go wrong since the inner workings have become invisible :-(

As far as bus lanes go, it looks like the easiest thing to do is use 
'busway' with exactly the same tags as cycleway. So once the sidedness 
problems are resolved for cycleways busways will be fine too. In the 
meantime I guess I'll hold off and start mapping historic buildings 
instead ;-)

Graham

> </plug>
> 
> Gerv
> 
> 
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