The potential problem I see is when you have a road that alternates
frequently between single- and dual-carriageways (which many state
routes do, and even a lot of US highways). How do you represent this in
a single relation?
1) Put single-carriageways in once, with no role. Or, with
"role=north/south". Either way, this is difficult to recognize and
parse automatically. And aren't members of a relation ordered inside
the relation? (I know JOSM shows icons for whether a way is connected
to the ways before and after it in a relation.) The ordering loses any
meaning under this method.
The way I've done this, and seen it done, is to put single carriageways in
once with no role. I'm not sure I understand the difficulty of parsing
it automatically - please elaborate.
Ordering has no meaning in road route relations. JOSM can sort them as a
debugging tool. Ordering is too easily lost, as seen in the constant loss
of bicycle route relations sort order in Europe.
In my view, having separate relations for each direction, and a
super-relation to hold them solves this problem. But maybe there's some
argument against them that I've missed.
It certainly will work also - my only complaint is juggling the 3
relations in the editor. Perhaps this won't be a problem after the road
network is comprehensively tagged.
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