So I understand that one-way ways carrying a route (e.g. a one-way pair or
divided highway) should have relation roles of north/south/east/west, but say
you have a situation like this. Say you have an east-west route that follows
the primary roads in that picture. The eastbound direction follows the
channelized right turn slip ramp, marked with a red arrow. The westbound
direction follows the blue-arrow way, before turning left onto the green-arrow
way.
How should relation memberships and roles be assigned here? I would think that
the slip ramp would be part of the relation, since right-turning traffic must
follow it. Ideally, that would be given the role "east", but what about the
green and blue ways? It might seem right to give them the role "west", but how
then is it differentiated which direction is westbound for it? Since all the
ways in this picture are arranged "pointing" north or east, the green and blue
ways would need to be given the role "backward", which is the older way of
doing things that can't specify cardinal direction. Is replacing the single
relation with separate relations for each direction the only good way to do
this, or are such two-way segments the only times that "forward" and "backward"
roles should be used?
I checked the wiki page, but it doesn't seem to specify. Instead, it just says
such cases are very rare (which is only true relatively speaking, as routes
very commonly turn at intersections with channelized right turns, making
situations like the linked example very common.
--Roadsguy
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