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
>
_______________________________________________
Talk-GB mailing list
Talk-GB@openstreetmap.org
https://lists.openstreetmap.org/listinfo/talk-gb

Reply via email to