[Tagging] Tagging split exit ramps

James Mast rickmastfan67 at hotmail.com
Mon May 16 02:33:31 BST 2011

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 		 	   		  
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