[talk-au] maxspeed - best practice?

Ben Johnson tangararama at gmail.com
Tue Aug 14 16:44:44 BST 2012


On 14/08/2012, at 16:44, Ian Sergeant <inas66+osm at gmail.com> wrote:

> Hi,
> a) The thing is, if you don't tag maxspeed=50, then how do tell a residential road that is known to be maxspeed=50, against one that is just un-surveyed, and might be maxspeed=30,40 or 60?

Yes... always the exceptions that create the mountain of work!


> c) source:maxspeed=sign is clearly correct if there is a sign. If you've surveyed around an area, and there isn't a sign, personally I'd tag source:maxspeed=survey.  The alternative here, would be source:maxspeed=default or some such, but given our history of tagging "site unseen".   It  I think this is best avoided. Same goes for source=implied for the same reason.  If you've visited and determined the speed limit, it is a survey.   maxspeed=local_knowledge if you drive around the residential streets in your area all the time, and you just know they are all 50km/h.

That's a tidy differentiation between sign, survey and local_knowledge.  I've sometimes struggled with the differences. From now on I'll refer back to this!  We need to get this onto the wiki.

On the subject of tagging "site unseen"... you brought up a perfectly legit point about routers and efforts made in the past to assist routing engines. I'm just trying to get a sense where our community stands in relation to maxspeed tagging "site unseen", for residential streets, and how we identify such tagging.

Im thinking one of these might serve that purpose...

source:maxspeed=default
source:maxspeed=unconfirmed
source:maxspeed=fixme
source:maxspeed=presumed

It would be a stop-gap measure to assist routing engines, and we can later use such tagging to flag areas needing proper survey. And then there's the aspect that once something is surveyed, it needs periodic review ... but that's a whole new consideration.


> Just an aside,  a simple case study in presumptions.  Probably the most popular OSM open source router is OSRM.  The speedprofiles for that project you can see here
> 
> https://github.com/DennisOSRM/Project-OSRM/blob/master/speedprofile.ini

Thanks. I knew this existed somewhere... but had no idea it was using 25! Clearly there's too many exceptions and unknowns - even if the profile was on a country-by-country basis, we have layers of government authorities wanting to set their own rules and it's forever changing.

BJ




> 
> I believe OSRM will use a maxspeed on a street if it finds one, so once you start marking maxspeeds it makes sense to mark others around them, otherwise a maxspeed=40 road will become a preferred road over other residentials and secondaries.
> 
> I'm sure the motivation for tagging all residentials as maxspeed=50 was partly an attempt to address this issue. 
> 
> Of course, there is a good argument for this being fixed in OSRM, or in post-processing the AU data, etc.
> 
> Ian.
> 
> On 14 August 2012 15:30, Ben Johnson <tangararama at gmail.com> wrote:
> In regards to residential areas - I remember last year there was some talk about the bot that added "50" with the (incorrect) "maxspeed:source" key = "default residential speed limit in Australia"  and I think there was consensus in the local community that this was a mistake.
> 
> With remapping some of my local areas, I'm now curious what's best practice in Australia is for tagging maxspeed on residential streets. Specifically...
> 
> a) is it even necessary or desirable to explicitly define maxspeed for every residential way - or should we just presume any highway=residential is maxspeed=50, unless otherwise stated?
> 
> b) if presumptions do exist, should 50 zones on tertiary and unclassified ways be explictly tagged ?
> 
> c) if tagging maxspeed on every street, in respect to source... does a simple source:maxspeed=sign suffice for the "general area" or only for the specific way on which the sign is placed?  I notice these residential 50 speed signs are often on tertiary streets, or gateway points into general residential areas.  Side-streets obviously share the 50 limit, but are mostly not signposted. Do we need a new standard source value like source:maxspeed=implied for the side streets ?
> 
> Sorry if I'm re-covering old ground - I'm just not sure where it was left... if anywhere!
> 
> Thanks in advance.. BJ
> 
> 
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