[talk-au] maxspeed - best practice?

Ian Sergeant inas66+osm at gmail.com
Wed Aug 15 05:27:05 BST 2012

Ben Johnson <tangararama at gmail.com> wrote:

> 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.

Just to be clear, I'm totally against speed limit guessing based on
highway=* type.  (site unseen maxspeed tagging).

I understand the motivations: that you don't have to change the
router, that it encourages corrections and more maxspeed info to be

It is just that adding potentially millions of default maxspeed tags
to residential streets, rather than adding one line of code to a
router or exporter seems totally skewed to me, especially when in most
case the routing applications will work just fine on residential
streets (mostly non-through ways, after all) without this information.
 Most routers aren't (and shouldn't be) directing people to use
residential streets as through routes.  Routers presuming a too low
speed for residentials (the speed in AU is relatively high) usually
yields a satisfactory outcome even when the residential roads don't
have a tagged maxspeed.

Well intentioned default speed tagging may in fact have the opposite
effect, for example in the OSRM default configuration it will cause
routing to use residential roads tagged with maxspeed=50, rather than
taking a tertiary road with a lower default maxspeed.

My only concession to routers, would be that if you maxspeed tag a
residential street you should try and also tag the connecting ones if
possible, so that routing anomalies don't happen due to speed


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