[Talk-GB] Maxspeed tagging for the UK

Peter Miller peter.miller at itoworld.com
Thu Apr 14 12:13:32 BST 2011

On 14 April 2011 11:42, Richard Fairhurst <richard at systemed.net> wrote:

> 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?

You note below the difficulty of establishing exactly what is a one way road
and what is part of a dual carriageway. That is one complication that is
worth remembering.

There is also the difficulty of identifying which country you are in and
therefore what lookup value you should use. Does the Ilse of Man have the
same rules as England? Northern Ireland? Jersey? I have no idea and nor
would someone from Japan.

There is current the problem that no one has actually created a look-up
table for the values that can be used by downstream systems and that is very
hard to do when the rules for each country are different and when there is
not even agreement on the tags within a country.

You point about tagging for the mapper. I think it is shortsighted to tag in
such a way that the downstream applications have a problem and indeed either
ignore the data at all or get it wrong. If we did that universally then the
UK would be the only ones using highway=motorway and Mapnik would need loads
of rules to deal with highway=interstate, highway=autobaun,
highway=autoroute etc etc.

To respond the monxton either of the proposed systems will accommodate
changes to rules as occurred in 1970s. Without a clear distinction about the
jurisdiction and the exact distinction between a single and dual carriageway
it can not.



> cheers
> Richard
> [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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