[Tagging] Tagging average speed [Was: Re: Residential roads]

Anthony osm at inbox.org
Sun Oct 3 16:30:11 BST 2010


On Sun, Oct 3, 2010 at 11:16 AM, Ralf Kleineisel <ralf at kleineisel.de> wrote:
> On 10/03/2010 05:04 PM, Anthony wrote:
>
>> Maybe it's just because of where I live, but I don't see how it would be.
>
> Well, where I live (Germany) we have a legal limit of 100 kph on roads
> outside of cities, motorways excluded. This legally applies even to
> small roads if there is no sign indicating a lower limit. On many roads
> you can achieve this speed, too. But on the other hand we have lots of
> narrow, twisty country roads where a normal driver does not go faster
> than 60 kph. In the Alps it is even more drastic. For estimating the
> time someone will probably need to drive along a road this information
> would be very helpful.

That seems like a reasonable argument to me.  I'd question whether or
not we'd want to call it "average speed" though.  If we limit the use
of it to roads which are structurally of a nature which doesn't allow
safe driving at the speed limit, I don't think we'll get into those
problems I mentioned above.  What I'm most hesitant about is if you
factor in traffic.  Traffic is too transient (and contains too much
time-specific data) to be put in OSM, unless the whole structure of
OSM is redesigned.

> Even if we introduce this tag, nobody is forced to ever use it.

That's one of the big potential problems, actually.  If you have
average speed information on some ways, and no average speed
information on other ways, there's going to be a systematic bias in
the routing algorithms either to use or to not use ways with average
speed information.  (Unless the routing algorithm can perfectly
predict the average speed of ways without average speed information,
in which case the average speed information is useless anyway.)

Unless the tag is used consistently, at least consistently across any
particular geographic area, it's going to be more trouble than it's
worth.



More information about the Tagging mailing list