Motorway junctions where the slow lane seperates from the through lanes

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Motorway junctions where the slow lane seperates from the through lanes

Mike Parfitt
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.
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Re: Motorway junctions where the slow lane seperates from the through lanes

Paul Berry
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 <[hidden email]> 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.
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Re: Motorway junctions where the slow lane seperates from the through lanes

Ed Loach-2

See also

https://wiki.openstreetmap.org/wiki/Lanes

which has some quite good notes on how to map lanes. I suspect this is how OsmAnd knows to give me lane guidance (can’t think how else it could know).

 

I suspect based on that you’d want to begin your new way for the drop lane where the lane splits away from the main carriageway, with an earlier split for lanes=3, turn:lanes=slight_left|through|through with lanes=1 on the new way and lanes=2 on the main way after the split.

 

Ed

 

From: Paul Berry
Sent: 14 January 2020 13:15
To: Mike Parfitt <[hidden email]>
Cc: [hidden email]
Subject: Re: [Talk-GB] Motorway junctions where the slow lane seperates from the through lanes

 

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 <[hidden email]> 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.

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Re: Motorway junctions where the slow lane seperates from the through lanes

Mike Parfitt
Have a look at www.openstreetmap.org/changeset/79582073

On my Samsung Tablet I have been using Bing satellite images with the Vespucci editor, but other images also show the road markings quite clearly.
From: Ed Loach <[hidden email]>
Sent: 14 January 2020 13:45:34
To: 'Paul Berry' <[hidden email]>; 'Mike Parfitt' <[hidden email]>
Cc: [hidden email] <[hidden email]>
Subject: RE: [Talk-GB] Motorway junctions where the slow lane seperates from the through lanes
 

See also

https://wiki.openstreetmap.org/wiki/Lanes

which has some quite good notes on how to map lanes. I suspect this is how OsmAnd knows to give me lane guidance (can’t think how else it could know).

 

I suspect based on that you’d want to begin your new way for the drop lane where the lane splits away from the main carriageway, with an earlier split for lanes=3, turn:lanes=slight_left|through|through with lanes=1 on the new way and lanes=2 on the main way after the split.

 

Ed

 

From: Paul Berry
Sent: 14 January 2020 13:15
To: Mike Parfitt <[hidden email]>
Cc: [hidden email]
Subject: Re: [Talk-GB] Motorway junctions where the slow lane seperates from the through lanes

 

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 <[hidden email]> 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.

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Re: Motorway junctions where the slow lane seperates from the through lanes

Neil Matthews-2
In reply to this post by Mike Parfitt
This is a changeset that is under discussion:
https://www.openstreetmap.org/changeset/79260663#map=16/51.5089/-2.5232

The disagreement is that there may be the start of an "exit lane", but
there is no physical separation where the junction has now been modified
-- see the changeset dicsussion for background info.

Local mappers would prefer that the junction were to be split where
there is a physical, rather than a logical separation,
https://wiki.openstreetmap.org/wiki/Editing_Standards_and_Conventions#Divided_highways

Cheers,
Neil


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Re: Motorway junctions where the slow lane seperates from the through lanes

Paul Jaggard
In reply to this post by Mike Parfitt
Hi


I would suggest that the motorway should not be split until the point
where the two halves physically diverge; instead, where there's a drop
lane, use turn:lanes and destination:lanes tags to indicatethe presence
of the drop lane.

My reasoning for this:

- firstly, there's no physical separation between the drop lane and the
main line of the motorway, and it's still physically and legally
possible to change between the two, and

- secondly, splitting a motorway based on different lanes having
different destinations sets an awkward pattern, which taken to extremes
means we end up splitting roads all over the place based on lane
markings.  Sometimes that's necessary to make routing work sensibly
through complex junctions, but I'd argue that this isn't one of those cases.


Best illustrated with examples:

Drop lane starts here.  Before this point, a single way with lanes=3. 
After this point, still a single way, with lanes=3,
turn:lanes=slight_left|through|through :

https://www.mapillary.com/app/?pKey=v4H-uhxh9QQYjzL1b_BNMg&focus=photo

The drop lane then runs for 300 metres, where there's no physical (or
legal) barrier between the lanes, so still a single way with lanes=3,
turn:lanes=slight_left|through|through :

https://www.mapillary.com/app/?pKey=S-dGYQdsR7olODRufbB5bg&focus=photo

Then the actual split, where first there's a legal barrier (solid white
paint), then a physical one (grass, barrier, trees, hillside, etc):

https://www.mapillary.com/app/?pKey=1WY5HbP5K-vpUnAT0voYGw&focus=photo

It's here where I'd suggest we'd split into highway=motorway_link,
lanes=1 (lanes=2 shortly thereafter), and highway=motorway, lanes=2,
with a shortish Y-shaped transition to make it look sensible.  Of
course, at this point the main line of the motorway loses the turn:lanes
tag, and you can then add turn:lanes tags to the slip road as it widens
out for the roundabout at the end.  The middle point of the Y (and not
the start of the drop lane) carries the highway=motorway_junction and
associated tags.

You could also add destination:lanes tags to label up the signed
destinations, and destination:ref:lanes=A4174|M32|M32.


Incidentally, for me, /this/ is the sort of situation justifying
separate, parallel ways on a motorway:
https://www.mapillary.com/app/?pKey=AL0RC-DyWe27PMQEAS1uZA&focus=photo


TL;DR?  Don't split based on lane markings, it's not a 300-metre-long
physically separate way, it's just a lane with a different destination. 
Instead use turn:lanes, destination:lanes and destination:ref:lanes tags
to indicate the drop lane.


Cheers,


Paul ("southglos")



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