Hi Mike, Interesting points and no easy answer I fear.
I think in mapping terms the midlines of each carriageway after the diverge will look more like a upside-down Y and I tend to do a bit of smoothing to make it look less abrupt. I think this is what you're getting at (apologies if not). It's not dissimilar to the situation where a single-carriageway road splits around an island: because the way is drawn as a line—not an area—the carriageway split is always going to look more dramatic drawn that way compared to the smooth continuous reality of what's on the ground. In the situation of a lane drop don't forget to keep track of the lanes=<num> in the keys. It might be easier if you just go ahead and map as you see fit then post the changeset link if you want further commentary. Regards, *Paul* On Tue, 14 Jan 2020 at 08:26, Mike Parfitt <m_parf...@hotmail.com> wrote: > The technical term is a drop lane. This might later intersect with a > roundabout, join with another motorway or primary road etc. Between > junctions, a single way for each direction is commonplace. At junctions, > there are ways for the through lanes and for traffic exiting and entering > the motorway. > > For example, on a 3-lane motorway with 3 lanes going in one direction and > no junction anywhere near, the way would typically be placed along the > centre of lane 2. > > However, when lane 1 is designated as a drop lane, what was being mapped > as 1 way needs to split into 2 ways. > > The question is where ? > > There are various anticipatory changes in road markings well ahead of the > physical separation of the asphalt, together with blue and white signs, > some of which precede the first of the changes in road markings. > > In the case described above, my convention is to pick the start of the > shorter dashes between the drop lane (1) and the through lanes (2 and 3). > From then onwards, the way for the through lanes is mapped along the longer > dashes dividing lanes 2 and 3, while the way for the drop lane is mapped > along the centre of lane 1. > > Others do it differently. > > See "https://www.gov.uk/government/publications/traffic-signs-manual" > from where you can download "Traffic signs manual chapter 5 road markings > (2019)" which is a PDF. Page 82 contains figure 7.7 and text documenting > drop lane road markings. > _______________________________________________ > Talk-GB mailing list > Talk-GB@openstreetmap.org > https://lists.openstreetmap.org/listinfo/talk-gb >
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