[Talk-GB] Maxspeed tagging for the UK
richard at systemed.net
Thu Apr 14 11:42:52 BST 2011
Peter Miller wrote:
> So the proposal is now:
I may be missing the point on all of this, but:
Why are we doing this?
In OSM we optimise for the mapper, not the data consumer. That means we tag
exceptions, not majorities.
So if you have highway=motorway, the consumer can assume the national speed
limit applies, which is 70mph; no need for a maxspeed or maxspeed:type tag.
If you have highway=trunk (or anything down to unclassified), assume the
national speed limit applies, which is currently 60mph if it's a single
carriageway, 70mph if it's a dual. And so on.
Where this isn't true, you put a maxspeed tag on. This works for pretty much
everything from 30mph on B roads through villages to 50mph on rural A roads
to 70mph on the A55 Special Road. No need for a maxspeed:type tag at all.
Have I missed something blindingly obvious?
 Perhaps the only difficulty is that there's currently no trivial way to
identify what's a dual carriageway and what isn't, short of doing clever
geometry stuff. But that's easy to fix: either a relation (spit) or
preferably something simple like dual_carriageway=yes.
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