[Talk-us] Relation roles for two-way way segments carrying routes in a single direction

Albert Pundt roadsguy99 at yahoo.com
Mon Dec 26 17:29:08 UTC 2016


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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