On 11/06/2010, at 12:13 PM, John Smith wrote:
On 11 June 2010 11:45, Simon Biber simonbi...@yahoo.com.au wrote:
My personal preference would have been to use give_way, since it follows
the tradition of using British English as the source of tag names, but the
majority of mappers so far have chosen yield.
I've already shifted giveway to give_way and wrote a wiki page, since
there was none for yield and and doesn't help when I did a search of
yield in xapi I came up with nothing because I switched the i and e
around...
http://wiki.openstreetmap.org/wiki/Tag:highway%3Dgive_way
I wouldn't consider ~100 sign indicative of much, other than a lacking
of presets, I could easily bump highway=give_way up by marking every
intersection in the suburb, which is why I brought this thread up in
the first place... :)
Ah, this old chestnut - it's been debated a few times before on talk (or maybe
later tagging) list. There are several methods people use, which are mostly
non-conflicting. Below is a hopefully non-biased summary of the options, then a
completely biased argument from me:
1) The original, highway=stop (and =giveway/give_way/yield) on an intersection
node. The big problem is that you can't say who has to stop, so it can only
really represent all-way-stop situations.
2) highway=stop (and give_way) on nodes just back from the intersection
(usually level with the sign or road markings), applies at the closest
intersecting way[0]. Solves the main problem of (1), but you can no longer tell
what affects a way just by looking at the way and it's nodes.
3) stop=w,e;give_way=ne and similar on the intersection node. Solves problem
of (1) unless the roads join close to parallel and you can use nne if
necessary. Requires heuristic guesses about what roads it applies to (easily
done, some people object on principle). Some inconistency in current use about
whether you use ns or n;s, so you can't tell without looking at the way
locations whether ne is one road or two.
4) A stop=start/end/both tag on the way. Simple, but break horrible if someone
splits the way into two without fixing it.
5) A 'stop' relation which contains the roads that have to stop and the
intersection node(s). Can represent extra information such as stop if the
traffic lights are out or that it only applies in certain hours, but no-one
uses this at present. Arguably an unnecessary relation depending on how you
feel about relations
6) A 'traffic_control' relation which is the generalisation of (5), same
arguments apply. No more complex than (5) but can represent stop, give way, and
other things in a single relation.
7) stop=all or stop=yes on the intersection node
And there may be others.
Statistics (from XAPI at 8:30 this morning) and links:
(1) and (2) 13559 uses, a quick random sample of 30 has most of them being (1),
even though some of them aren't all-way-stopswhen yu look at Google Street View
:( http://wiki.openstreetmap.org/wiki/Tag:highway%3Dstop
(3) 122 uses of stop=*, 0 of give_way=*, not documented AFAIK
(4) 768 uses, a mix of stop=yes/both/all/-1, most applying to multiple
intersections http://wiki.openstreetmap.org/wiki/Tag:highway%3Dstop
(5) 457 relations for 523 ways
http://wiki.openstreetmap.org/wiki/Proposed_features/Relation:type%3Dstop
(6) 197 relations for 228 ways
http://wiki.openstreetmap.org/wiki/Proposed_features/Relation:type%3Dtraffic_control
(7) 19 uses. plus 6 stop=both in four-way intersection nodes,
http://wiki.openstreetmap.org/wiki/Tag:highway%3Dstop
(1) is easily the most popular (it's been around the longest) but it can't
accurately represent a lot of things, and people use it incorrectly. If someone
wants to know how many (2)s there are, they can go script up a check whether
the highway=stop nodes are on intersecting ways or not.
I think everyone agrees (1) isn't good enough, as it can't handle the simple
case of one road having to give way to another, and that (6) is obviously
better than (5) because it handles more with no additional complexity. The
remaining choices depends on what your opinion on relations is, and whether you
view these as separate traffic must stop POIs or a single traffic control at
the intersection thing.
Personally, I think that this is an okay use of relations and tend to see it as
a single traffic control at the intersection thing. So wrote the wiki page
for (6) after chatting with a few people on IRC a while back and use that. I
know John and others favour (2) and there are people who use all the others too.
[0] Some debate about whether this means the closest intersecting way, closest
intersecting highway=* way or closest intersecting road-type highway=*. If a
footpath/cycleway crosses the road, traffic has to give way to them as well as
to the vehicular traffic, so can require some heuristic guesses, but it
shouldn't be that much of a problem in practice.
-- James
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