[Tagging] Tagging 'advance' turn restrictions

[Kevin Kenny]

On Wed, Apr 5, 2017 at 6:29 PM, Tom Pfeifer <t.pfeifer at computer.org> wrote:

> On 06-Apr-17 04:09 AM, Kevin Kenny wrote:
>>
>>> Do we have a scheme for tagging such a beast?
>>>
>>
> You can combine turn:lanes [1] with change:lanes [2], the first describe
> which lane you have to use for which turn, the second where you can change
> lanes and where not.
>
> [1] https://wiki.openstreetmap.org/wiki/Key:turn
> [2] https://wiki.openstreetmap.org/wiki/Key:change
>
> If you want to show us the current situation, you can drive along with the
> mapillary app and upload, so you don't need to show outdated G*****
> pictures ;-)
>

Before doing the Mapillary thing, I have to rig a dashcam first, or at
least have a passenger. The one series of Google pictures showing the signs
was at least to explain the idea.

The combination of turn:lanes and change:lanes sounds plausible, if it will
actually work. I presume that the routing and navigation systems[1] have
some presuppositions about lane continuity through an intersection? Let's
say that I have a setup where A is the stem of a T intersection while B and
C are its left- and right-hand branches.

On A I have tagged:

lanes=5
lanes:forward=3
lanes:backward=2
turn:lanes=right|through|left|left|right
change:lanes=yes|yes|no|no|no

I suppose, given the signage, I could add
direction:lanes=||Union Street|Seward Place|Union Street to indicate what
the overhead signs say.

On B I have
lanes=4
lanes:forward=2
lanes:backward=2
turn:lanes=right||through|through;left|right
change:lanes=yes|right_only|no|no

In short, I have two lanes turning left from the forward direction of A
into the forward direction of B, and the two lanes of B go through;left and
right respectively at the next intersection.

Presumably, a routing and navigation system will expect that the leftmost
lane of A will become the leftmost lane of B after the turn, while the
center lane of A will become the right lane of B? That's the only way I can
see this scheme working.  It would involve some fairly tricky graph-tracing
to deduce that a vehicle planning to turn right after B must be in the
center lane approaching A, but I suppose that sort of thing is what routers
are good at. Then a navigation system could announce, "Take the center lane
and follow signs toward Seward Place".

I'm guessing, considering the diversity of responses, that this
functionality is slightly beyond what our actual navigation systems have to
offer at present, but it at least gives me hope for a path forward. I may
or may not trouble to tag these things, since I suspect they will change
again before there's an actual data consumer for them. At least, I can see
that it's possible.

I had either missed 'change:lanes' altogether, or else had seen that it was
languishing in 'Proposed' status and moved on.
----
[1] Yes, I understand the difference, but don't always spell out the whole
phrase - when I said 'router' I really meant the whole stack.
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