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The book OpenStreetMap: Using and Enhancing the Free Map of the World by Ramm, Topf, and Chilton (urn:isbn:978-1-906860-11-0) suggests using relations with There are currently 997 uses of this tag for relations in the OSM database, but no machine-accessible documentation, so I might upgrade the proposal for it to something documented as a de facto tag. |
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In mind is that in the UK, roads (excluding motorways) specifically marked as a dual carriageway would be subject to a national speed limit of 70 mph for cars, and 50 mph for HGVs; compared with 60 and 40 on single carriageways. These would be usually signified with a 'dual carriageway' sign at the commencement, and the upside down Y sign at the end (as opposed to the two way traffic sign, which may be used additionally to provide a further warning. Short separated ways at say, intersections, as far as my understanding of traffic laws goes at least; would not be a type of dual carriageway, and would therefore have the lower limits - therefore the tag should probably be documented properly. Cheers Chris |
