[Tagging] unclear motorway_junctions

[Peter Budny]

Nathan Edgars II <neroute2 at gmail.com> writes:

> So highway=motorway_junction applies to a node, and helps routing
> software by giving it the junction number to tell you to exit at.
> Presumably said software would assume that if there are three legs at
> the intersection, two non-links and one link, movement onto the link
> is taking the exit. But this isn't always going to be true; one might
> have all legs non-link (a major split signed as an exit from one
> route: http://www.openstreetmap.org/?lat=28.85883&lon=-82.09167&zoom=16&layers=M)
> or two links (a split at the end of a route:
> http://www.openstreetmap.org/?lat=27.89497&lon=-82.50818&zoom=17&layers=M
> currently tagged with exit 1A where that side of the split curves away
> from the once-proposed extension, but it would more correctly be at
> the same place as exit 1B:
> http://www.southeastroads.com/blog/fl-618_wb_exit_001b.jpg). Would I
> want to use http://wiki.openstreetmap.org/wiki/Relation:destination_sign
> for this, or is there a simpler way?

I've been thinking for a while that there are enough situations where
it's unclear how to describe an intersection that there should be a tag
for specifying this.  You can't ALWAYS tell from the map whether
something should be "left", "slight left", "bear left", "go right on the
jughandle then go straight", etc.

Example: if two major highways split, does the sign indicate that they
are left-and-straight?  Straight-and-right?  Left-and-right?  You can't
know that just from the angles and highway=* tags.

I don't think the destination sign relation is quite for this... that is
(I think) more for having your satnav say "follow the signs for
Kalamazoo" and let you figure it out from there.  What I'm thinking is
more so that it knows how to describe a turn the way signs or local
residents describe it, which I think is what you're looking for.
-- 
Peter Budny  \
Georgia Tech  \
CS PhD student \