[Talk-GB] inferred single-carriageway NSL?

[Richard Bullock]

> 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?

I can certainly do that. I believe this one was places to "remind" drivers 
that, despite having four lanes, it's still a single carriageway and => 
60mph max

http://tinyurl.com/6x5u4la

In this case, it's probably technically "national", but specifically signed 
at 60.

I know of a couple of examples of cases on a dual-carriageway where it's 
specifically signed 70mph AND most definitely not the national speed limit.

http://tinyurl.com/66pucm7

The reason it's not the national speed limit, is because of the way that the 
legal orders that created this stretch of road were drawn up. In this 
particular example, this type of road has no national speed limit - and a 
white sign with black diagonal line would mean genuinely derestricted. (It's 
a non-motorway special-road in case you're asking - and special-roads only 
have a national speed limit if they are also motorways - hence a specific 
70mph speed limit order had to be drawn up).

Back to the point in question, however;

Do we *really* need to be tagging national speed limits on individual ways? 
E.g. the vast majority of roads ought to be one of;
*residential roads subject to 30mph
*rural roads subject to NSL

(I realise a lot of councils have been cutting lots of roads from NSL -> 50 
in recent years, but I'm sure NSLs outnumber 50s on the whole)

Perhaps we could tag the ones that differ from the above - and let 
post-processors add national defaults as necessary?

Taken to its extreme, are we going to bother adding surface=paved to every 
motorway, motorcar=yes to every road?