Peter,
After your first post on this, my initial thought was that you were
correct and the simpler tag you were proposing was enough. I started
following your proposal, but I've thought a little more & feel that the
more involved 'GB:nsl_single' type tag is actually needed & I'll be
going back through my work over the last couple of days and changing it
back.
My thinking is;
i/. The basis of GB law is that it is up to the individual to know what
the law states, and to comply with it. No matter what your SatNav tells
you it won't help you when you are standing in a court explaining your
actions - the SatNav is a guide only and some maintain that they are
unsafe as they distract the driver who may therefore miss the speed
limits being displayed.
ii/. If you are driving a motor vehicle with very few exceptions you
should comply with the law regarding speed limits.
iia/. A built up area with street lighting (I'm not entirely sure
how you define built up area, and I seem to remember something about the
street lights being no more than 200 yards apart) will have a speed
limit of 30 mph unless there are signs indicating otherwise, & there
should be repeater signs at intervals if it is not a 30mph area.
iib/. National speed limit signs - the national speed limit has
changed during my lifetime. Motorways are fairly simple, and for a car
(not towing) it will be 70mph. Two-way roads with a national speed limit
sign are also fairly simple, being 60mph for a car (not towing). Dual
carriageways - little bit more complex - an island in the middle of the
road to assist pedestrians to cross is not sufficient to make it a dual
carriageway, but you would need to look at the current case law to help
in deciding what exactly is a dual carriageway. I don't think a long
length of wide road with the lanes divided by white crosshatch markings
on the road, even if this exists for a length measured in miles, counts
as a dual carriageway - it needs to have a physical barrier involved.
iiic/. A prescribed limit indicated by signs such as '40', '50' etc..
iii/. The current software writers who seem to be using OSM data are
mainly wrestling with the basics of navigating a car anywhere in the
world but I think steps are being made towards navigation for larger
vehicles, and these vehicles are likely to have different speed limits
imposed on them in GB national speed limit areas. If they are writing
software for navigating a 40 tonne lorry across Europe then the least we
can do is try to indicate what type of road it is so they can attempt to
give an indication to the driver of what is the maximum speed they may
legally travel at.
Regards
Nick
(Tallguy)
Hi Peter,
Thanks for replying here.
Peter Miller wrote:
So...on the basis that we should tag what is there, we see a white sign
with a black diagonal line on it then that is what we should indicate. We
do of course interpret that by putting what we believe if the correct legal
speed limit in maxspeed. As such a single carriageway national limit is
coded as "maxspeed:type=gb:national,maxspeed=60 mph". As dual carriageway
is tagged as "maxspeed:type=gb:national,maxspeed=70 mph". The motorway
version is "highway=motorway,maxspeed:type=gb:national,maxspeed=70 mph".
I understand the potential problem (does a national speed limit dual
carriageway slip road count as a dual carriageway or not?) but am concerned
that changing e.g. "GB:nsl_single" to "gb:national" will:
o potentially obscure any underlying data errors (imagine something tagged
"maxspeed=70 mph, maxspeed:type=GB:nsl_single")
o make things more difficult for data consumers (if only by changing the
data from something that they might be expecting)
o confuse new mappers who see data that they've entered being changed
because it's "wrong", when in reality there really isn't a concensus on
this.
I fully accept that national speed limit tagging in the UK is a mess (at
the time of writing 4 of the top 6 values for
http://taginfo.openstreetmap.org.uk/keys/maxspeed:type#values could mean
the same thing) but any consolidation must proceed following discussion.
Sure, and I am politely inviting people to discuss the subject now and am
suggesting that it makes a lot of sense to consolidate around a tag value
which describes what one sees in front of one on the ground, ie a black and
white sign. To be clear I in the habit of using the nsl_single and nsl_dual
format until PinkDuck politely pointed out that I was tagging some
slip-road etc incorrectly and we agreed that is made more sense to avoid
the confusion in the first place and use the simpler gb:national.
With regard to the other point:
For avoidance of doubt, all my edits have been fully manual.
I don't believe that anyone has suggested otherwise
I was responding to Roberts comment above that "I certainly don't think
there has been any discussion of or agreement for a mass mechanical edit to
change existing values."
although I have certainly suggested that you may not have visited all of
the places that you have been changing the speed limit for. There is
clearly a sliding scale between "I've surveyed an area, and everything that
I've edited is based on the results of that survey, aided by e.g. Bing,
OSSV, and other named sources" and "I've changed a bunch of tags worldwide
based on who knows what information without even looking where I've changed
them".
The wiki's "mechanical edit
policy<http://wiki.openstreetmap.org/wiki/Mechanical_Edit_Policy>"
(as currently written) suggests that changes of this type may be covered
("search-and-replace operations using an editor... unless your changes are
backed up by knowledge or survey") - I guess that it depends on what you
mean by "knowledge" **.
Clearly no-one's going to object to some tag-changing edits
(designation=public_fooptath to designation=public_footpath for example)
but in this case there's enough doubt - other mappers have said "I think
the changes should reverted" and "This tag is vital" in the replies to my
original mail.
Based on that, where you've changed e.g. "GB:nsl_single" to "gb:national"
would it be possible for you to revert your changes? There's clearly a
discussion to be had going forward about which one of GB:blah, UK:blah,
gb:blah and uk:blah we need to keep, but based on the replies so far there
doesn't appear to be a concensus to support merging of everything into
"gb:national".
I don't hear a clamoring for such a reversion, and indeed I don't think
anyone in OSM is sufficiently knowledgeable able the law to say for sure
which tag should be used in all cases as I have indicated above.
Peter
Cheers,
Andy
** In which case quite possibly mea culpa for the changesets that I refer
to
here<https://lists.openstreetmap.org/pipermail/talk-gb/2013-September/015227.html>-
it's not black and white.
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