Peter wrote: > As such, it seems unreasonable to ask a new mapper to great a situation requiring > a court case for every ambiguous section of road in the country to establish if they > are dual carriageways or single carriageways. This is why I suggest we use > GB:national to indicate that the speed is set by a black/white sign. > > We could however compromise and suggest 'GB:nsl_dual' where we know if is a dual > carriageway, 'GB:nsl:single' where we know it isn't and GB:national where we aren't > sure. > Alternatively, we could always use 'GB:national' for the maxspeed type and add > other tagging to indicate dual carriagewayness, either using 'carriagway=A/B' tag > or a relation with type=dual-carriageway or similar. > Or.. and this is the simplest approach in the short term as far as I can see which > I have been advocating, we can imply dual-carriagewayness by a combining a highway > tag with the tag pairs 'maxspeed=70' and 'maxspeed:type=GB:national'. I say this > because the '70 mph' value for maxspeed can only be used case where a road is a > dual-carriageway. As we get clearer about what constitutes a dual-carriageway or not > we then only need to change with speed between 70 mph to 60 mph. We can then > also populate approach dual-carriageway tagging on these roads.
I prefer your compromise method for the very reasons you mention about the ambiguous bits. On those bits you are either guessing what numeric value to put in the maxspeed value, or you are guessing nsl_single or nsl_dual (implying you are also guessing maxspeed). So if you've guessed the speed you can't mix that with maxspeed=60/70 mph to identify dual carriageway anyway, and having national shows where the ambiguities are better. So, use GB:nsl_single or GB:nsl_dual with the correct (car) maxspeed where they are known, and use GB:national where you aren't sure and put 60 mph to err on the side of caution until evidence proves it higher. Ed _______________________________________________ Talk-GB mailing list [email protected] https://lists.openstreetmap.org/listinfo/talk-gb
