[Talk-GB] National speed limit changes

[Robert Whittaker (OSM lists)]

On 30 September 2013 08:12, Peter Miller <peter.miller at itoworld.com> wrote:
> On 29 September 2013 10:05, Colin Smale <colin.smale at xs4all.nl> wrote:
>> How about saying that 70mph can only be valid on a way tagged as one-way?
>
> In a word, I believe the answer is 'no'. I say that because the legal
> definition of a dual-carriageway appears to be vague, with unclear
> edge-cases. There are certainly examples of one-way national speed limit
> trunk and primary roads which are not 70 mph.

But that's not what Colin was saying. He was suggesting, "70mph
implies one-way", not "one-way implies 70mph".

Or to put it another way, he was saying "70 is not allowed on a
two-way road" rather than "a one-way road must be 70".

> It is for these reasons that I advocate setting maxspeed:type simply to
> 'GB:national' and then interpretting it to the best of our current knowledge
> as a numeric limit in maxspeed. Possibly we should err on the side of
> caution with the numeric limit.

In that case, surely it is better to make use of the more definite
tags GB:nsl_single and GB:nsl_dual when we are sure of the type of
road (which will be the majority of cases), and only use GB:national
for the cases where we aren't sure.

(Ok, so you can work out which is implied by looking at the maxspeed
value, but that's additional work for data users, and means that it's
less clear how the mapper has come to their maxspeed conclusion. Also,
with your suggestion of caution on unclear cases, there would be no
way to distinguish between a definite single carriageway road and the
unsure situation, since both would use maxspeed=60pmh and
maxspeed:type=GB:national.)

On 27 September 2013 15:40, Peter Miller <peter.miller at itoworld.com> wrote:
>> 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.

If there have been bulk changes from more specific things like
"GB:nsl_single" to the more general "GB:national", then I have already
said in a previous message that I think those changes should be
reverted. There had been no previous discussion or agreement about
making the changes (which is reason in itself for reverting), and
there still doesn't appear to be a consensus. Also, it's arguably
loosing information (whether it's right or wrong) captured by the
original mapper. In almost all cases it will be obvious whether a road
is a dual carriageway or not. I don't believe the few edge cases
warrant removing the majority of good information.

Robert.

-- 
Robert Whittaker