[talk-au] maxspeed - best practice?

Ian Sergeant inas66+osm at gmail.com
Tue Aug 14 07:44:48 BST 2012


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?

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.

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


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.


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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