[talk-au] tagging giveway signs

[James Livingston]

On 11/06/2010, at 12:13 PM, John Smith wrote:
> On 11 June 2010 11:45, Simon Biber <simonbiber at 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