[Talk-GB] Maxspeed tagging for the UK

Richard Fairhurst richard at systemed.net
Thu Apr 14 11:42:52 BST 2011

Peter Miller wrote:
> So the proposal is now:
> maxspeed:type=GB:national_single|GB:national_dual|GB:motorway|GB:restricted

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[1]. 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?


[1] 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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