[Talk-GB] inferred single-carriageway NSL?

[Peter Miller]

On 16 March 2011 17:43, Ian Spencer <ianmspencer at gmail.com> wrote:

>  Kevin Peat wrote on 16/03/2011 17:27:
>
>
> On 16 March 2011 17:00, Peter Miller <peter.miller at itoworld.com> wrote:
>
>>
>>
>>
>> Then there are the '30mph' which should for consistency be '30 mph' (with
>> a space).
>>
>
> I don't see the point of editing just for consistency. Developers should
> handle leading/trailing spaces, or the lack thereof, and different
> capitalisation, as without any input validation the data will always be
> inconsistent.
>
>
>>
>>
>> Finally, I have a technical question on speed limits. What exactly is a
>> dual carriageway? Are the slip-roads between two dual carriageways also dual
>> carriageways (and therefore have 70mph limits) or are they not and are they
>> therefore 60mph limits? Similarly for short sections where a single
>> carriageway road divides for a short section.
>>
>>
> I am also curious about this. There is a dual carriageway near me that has
> 3 roundabouts along its length. Two of the roundabouts have signed 40mph
> limits but the third one has no signed limit. I assume the limit for that
> roundabout is 60mph?
>
> Kevin
>
>
> I think the definition depends on physical separation, so I'd say that the
> roundabout is 70mph as the two flows are still physically separated - OTOH
> there is a bit that isn't... generally the physical constraints of
> traversing a roundabout make this a moot point. A slip road is divided from
> oncoming traffic, so it would be deemed to be 70mph. Of course, a speed
> limit does not indicate a safe speed of travel, so if a policeman got upset
> at you, he has a variety of other tools in his armoury to exact a punishment
> for anyone who gets pedantic.
>
> If the carriageway divides for a short way, e.g. for a junction, then the
> speed limit rises. Similarly, if they illuminate a junction, with lights at
> the required spacing, it is a de facto 30mph. That is why you will normally
> find such sections of roads acquire repeater signs. (It is mistakenly
> assumed that the street light rule only applies in built up areas).
>

In summary, this little tag is much less simple than it may appear at first
glance! I am very interested in getting a fuller set of this data into OSM.
Thanks for the 'pedantic' examples of 60mph limits on dual carriageways.
Being pedantic back can anyone demonstrate the existence of a 60 mph sign on
a single carriageway road? It is only 60mph when combined with a single
carriageway road that chriscf is tagging with nation limit source tag (and
similarly for 70mph/dual carriageway). I hope he is not tagging 60 mph
limits on dual carriageways with his tags.

Coming back to the original chriscf question, this discussion only makes his
automated edits more clearly dubious.


Regards,


Peter





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