So what are we talking about? Intersections like this one, where one
or more dual carriageways come together at an at-grade intersection:
https://www.evernote.com/shard/s9/sh/6438c196-bb92-4f66-81dc-9b75186286ba/0e8f07ff527c6a85c0dec426b9b79f1e
One of my colleagues at Telenav has remapped this intersection as follows:
https://www.evernote.com/shard/s9/sh/3491f1fe-6afa-4571-bc43-7cb31c9c2625/9dd47d1445fdcf03d3f0bbd93b8e0f92
Hi Martijn: one thing "wrong" I do see at this particular
intersection are extraneous nodes with highway=crossing tags: two
extra ones on the (northerly) east-west ped-path and one extra one
each of the (westerly and easterly) north-south ped-paths. A fairly
minor error in the context of your larger question.
The main difference, and the source of some feedback we have received
over the past few days, is that the dual carriageway roads are
straightened out, creating multiple intersection nodes (4 in this
case) instead of the original single intersection node that connects
all the incoming and outgoing ways. That technique turns out to yield
more reliable and correct routing and guidance ('keep left, turn
right') through these intersections in our testing. But of course,
that cannot dictate how we map as a community, so let's discuss.
I do this myself on intersections which have complex "two-to-one"
lane collapses in one direction, or "two-to-three" lane expansions in
another direction, or even both. I agree with you that making lanes
which capture dual carriageway and multiple lanes like this
accurately represents what is on the ground better, is pleasing to
the eye both in an OSM editor and on an OSM rendering, AND likely
results in better routing algorithm results (e.g. for offering turn
directions). The wiki entry on Braided Streets notwithstanding.
Some of the feedback we have received about these edits points to a
statement on this wiki page:
https://wiki.openstreetmap.org/wiki/TIGER_fixup#Braided_streets: 'It
is a reasonable and well-used technique to bring the ways of dual
carriageways back to a single point at intersections to facilitate and
simplify the mapping of control devices and turn restrictions.' In my
mapping across the US, my personal experience has been that this
technique is in fact used, but the 'after' technique with straightened
out ways is actually much more common. I personally prefer that
technique as well - I think it is more pleasing to the eye, represents
what is on the ground better, and is and easier to read. So my feeling
was that this mapping practice would not be disputed. It turns out I
was wrong, so I want to see what the consensus is on mapping
intersections of this type - or perhaps there is none and we can work
together to get there?
I don't know what the solution is. It may be to coexist with BOTH
types and try to do the best that can be done by "smartening up"
routing algorithms to cope with EACH type of intersection as well as
can be technically achieved. That seems "long-term wise" given that
there will likely be both types of intersections entered into the
underlying data.
SteveA
California
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