I would not consider a roundabout or a slip road to be any different to that signposted. Whilst exceeding 60 on a roundabout is unlikely, I would consider the limit to be that of the road it is joining. In the days before the chopsticks signs on motorways, and still in Scotland, the 70 sign was at the start of the sliproad.
Phil -- Sent from my Nokia N9 On 27/09/2012 10:10 Robert Whittaker (OSM) wrote: On 26 September 2012 18:55, Peter Miller <peter.mil...@itoworld.com> wrote: > There does seem to be a a massive consensus around the world that maxspeed > should be used to hold a posted speed limit in km/h or mph as a numeric in > the local units. +1 > There seems to be a mood to use maxspeed:type for the supporting > countrycode:zone data here, although more people are using source:maxspeed > for this globally. I have continued to use maxspeed:type in my cleanup pass > because in a number of cases the source:maxspeed already contained something > like 'survey', 'sign at S end' or similar. > > I suggest that we raise a proposal at some point to migrate the zone > information to maxspeed:type, but lets not worry about that for now. I've always used source:maxspeed for this, as I was under the impression that that was the consensus. However, I've always felt it wasn't quite right, so I'd be more than happy to switch to using maxspeed:type instead, and don't object to anyone who wants to convert any of my previously added source:maxspeed=GB:* tags. > Based on the dilemma I have had numerous times in the past week to decide is > a slip-road or roundabout is technically a 60mph or 70mph I would suggest > that we produce some guidance on what value to use in various situations > (even though it is a bit irrelevant and nerdy for most situations we could > imagine). I tag slip roads at the dual carriageway speed if at least one end > is on a dual-carriageway. I tag roundabouts as 70mph if there are at least > two dual-carriageways attached to them. I use 60 mph in other situations. My understanding (which may be wrong) is that the Dual Carriageway speed limit applies only on roads where there are two separated carriageways, and not just a one-way bit of road. Since roundabouts arguably are a one-way loop, rather than having two separated carriageways, I'd say they have a national speed limit of 60 rather than 70. I think I'd also claim that slip-roads with at least one end on a non-dual carriageway would be 60 too, ie the 70 doesn't start until you're actually on the dual carriageway proper. Slip roads which result from one dual carriageway merging into another would be more of a grey area... Presumably this is something that we could check with an appropriate government agency, though, and then we'd be able to tag things correctly. > Given that it is not always 100% clear if a road is 'dual' or 'single', I > suggest that we simply use use a value 'UK:national' in maxspeed:type (or in > source:maxspeed). This would be in place of uk:motorway, uk:nsl_single and > uk:nsl_dual. To be clear, the tag should be uk:national not just national > given the strong guidance on the wiki and through usage that it is > appropriate to include a country-code prefix. BTW: I believe that the country code for the UK is "GB" so all the tags should be GB:* rather than UK:*. Secondly, in terms of making the tagging useful, I think it's highly desirable to be able to distinguish between motorway, nsl_single and nsl_dual. This is because some classes of vehicle will have different speed limits on different classes of road (so it would be good to allow routing tools access to the information), and also because the speed limits for one of more of the classes might change at some point in the future. (Ok, I think you could probably deduce the road class from the values of highway maxspeed tags, but I still think it would be better to have the information there explicitly to make it easier for data users and consistency checking.) Robert. -- Robert Whittaker _______________________________________________ Talk-GB mailing list peter.mil...@itoworld.com http://lists.openstreetmap.org/listinfo/talk-gb
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