[Tagging] Tagging split exit ramps

[David ``Smith'']

On Sun, May 15, 2011 at 9:33 PM, James Mast <rickmastfan67 at hotmail.com>wrote:

>  I was just thinking, here in the USA, we sometimes have exit ramps that
> after they split from the main highway, split again (sometimes with separate
> exit #'s).  One such example would be Exit #1B-1C (old #7A-7B) on I-279 here
> in Pittsburgh, PA.
> (Google StreetView examples from when the exits were still #7A & #7B:
> http://goo.gl/maps/ogTB & http://goo.gl/maps/kEqY)
> Right now, the current exit tagging scheme with the "exit_to" tag doesn't
> fully work for those kinds of exits because the destinations would be
> different for each ramp.  Same with the "ref" tag.
>
> I was thinking of "exit_to:left" and "exit_to:right" as well as "ref:left"
> and "ref:right" (also "name:left" and "name:right" for "named" exits if
> necessary).  This would also help for "motorway" splits where putting the
> current tag setup doesn't work at all (one such example would be the
> I-77/I-74 split in North Carolina: http://osm.org/go/ZS3WNy3x).  With that
> I-77/I-74 split, you can't tell (well, the data people can't easily tell)
> which highway the "ref" or "exit_to" tags go with (which is the left exit
> to I-74).  Places like that would greatly benefit from the "exit_to:left" &
> "ref:left" tags.  Heck, you could even then add "exit_to:right" for the I-77
> signs if you wanted to (or maybe even "exit_to:straight"?).
>
> I'm mainly putting this out there before I start up a proposal to deal with
> exits like this where we could then work with the renders and map data users
> to work up a scheme that would work for everybody.  Also, if you're
> wondering how the split exit numbers would be rendered, don't worry, there
> will be an example in the proposal if you guys think this is a good idea to
> go ahead with.
>
> -- James
>
>
I think the easiest remedy would be to make a slight change to how exits are
tagged.  I think there are currently two common approaches which may or may
not be combined: tagging on the way representing the exit ramp, and tagging
on the node where the ramp forks off of the mainline.  Perhaps it would be
better instead to put the relevant motorway exit tags on a node along the
exit ramp, just downstream from where it forks from the mainline.  In the
case of "split" ramps, the motorway exit tags would go on nodes just
downstream from where the two exits split from the same ramp.  This would
make it much easier for routing software to figure out whether or not they
should say "take exit ## towards ___" -- as it is now, MapQuest's directions
often say to take exits that it actually wants you to drive past, and
ignores exit designations for exits it really wants you to take.  This would
also make it easier to tag exits that split off of exit ramps which have
their own destination not even signed on the "parent" ramp, and make it
likely that routing engines would make sensible directions in such cases.
(Example in Columbus, good directions from the airport to Columbus State
Community College might include the following: "Take exit 5 / I-71, towards
Cleveland & Cincinnati. Take the left fork in the ramp, for I-71 South,
towards Cincinnati. Take the right fork in the ramp, for SR-3 & Cleveland
Ave...")

-- 
David "Smith"
a.k.a. Vid the Kid
a.k.a. Bír'd'in

Does this font make me look fat?
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