[Tagging] [Talk-us] Freeway exit tagging

Kieron Thwaites kieron.thwaites at gmail.com
Fri Aug 26 12:18:41 UTC 2016

I can't comment whether this is "proper" usage or not, but I can
illustrate how I've personally tagged lanes at freeway exits:

Take, for example, this freeway interchange close to where I grew up
(note: left-hand drive): https://goo.gl/maps/5eF35SVed452

There's no lane markings to indicate direction itself, but there is a
solid line starting a few hundred metres out and continuing just past
the ramp, indicating no lane changes from lane 2 to lane 1 (where lane
1 is the left-most lane).

There is, however, overhead signage for this particular interchange as follows:

https://goo.gl/maps/ApFqTg7vRQT2 (1 km out)
https://goo.gl/maps/FTtiG5UHaxx (500 m out)
https://goo.gl/maps/VMw9Rcpsua62 (at the ramp)

The sign 500 m out is the key one -- that's the one that has the turn
lane information on this.  As such, were I to add turn lane data in
this area (I wouldn't, as I moved out of that city in 2010 and don't
consider myself to have sufficient local knowledge there any more),
I'd tag as follows:

>From 500 m out until the point where the ramp separates:
The section with the painted lane restriction: change:lanes=yes|not_left|yes

Now, this is an urban setting and the overhead signage makes (to me,
anyway!) the tagging rather unambiguous.  In a rural setting however,
all you're likely to get is this:

https://goo.gl/maps/ajR1ccg6g252 (signage 1 km from ramp)
https://goo.gl/maps/NLm9VMNskKK2 (signage at the ramp)
https://goo.gl/maps/6aE1NbsuguG2 (overhead view of the ramp)

There's no explicit lane markings here, but once again, there's a
painted line indicating no lane changes from lane 2 to lane 1 around
the vicinity of the ramp, which implies
turn:lanes=slight_left;through|none (and of course, explicitly
specifies change:lanes=yes|not_left), so even through turn:lanes are
implicit on the ground, I'd explicitly tag it.  I personally see this
as unambiguous as per the urban example.

Now, when it comes to the US example that Jack posted
(http://mapillary.com/map/im/7igAGXSa6EsUYlTIujXchw), it seems like
there's nothing explicit or implicit, either from painted markings
(either arrows or lane change restrictions) or signage (I jumped on
Streetview and the only other sign I noticed was an "exit in 0.5 mi"
sign, similar in nature to my rural "exit in 1 km" sign).  In this
case, I would side with "through;slight_right" -- even though there's
nothing explicitly or implicitly specifying as such, the reality on
the ground appears that one can only exit from the right-most lane
while continuing to continue through, and the remaining lanes are for
through traffic only.

I can, however, see the rationale behind tagging "none;slight_right",
as well as tagging nothing at all, and as such, I think that this is
an issue that we need to find consensus on.  That said, I believe Paul
is quite correct with his statement that machines "need to be told
about these restrictions in order for them to be able to provide
useful feedback from it" -- something that isn't explicitly present
(or maybe not even implicitly so) but appears obvious to a human on
the ground isn't necessary obvious to a machine.


On 26 August 2016 at 08:37, Paul Johnson <baloo at ursamundi.org> wrote:
> On Thu, Aug 25, 2016 at 11:06 PM, David Mease <meased3 at gmail.com> wrote:
>> Road markings are both beneficial and useful for navigation. Cities and
>> governments have paid a lot of money installing them all over globe
>> precisely for these reasons. OSM would be well served to include them
>> exactly as is. I don't hear a lot of people complaining about how those
>> arrows on the roads led them astray.
> Arrows on the road, at least in North America, are typically only installed
> to indicate relatively unusual lane restrictions, with the typical lane
> restrictions assumed to be common knowledge.  This is where this trips up
> automation, as machines need to be told about these restrictions in order
> for them to be able to provide useful feedback from it or lane guidance will
> be a NP-complete thing for data consumers to deal with.  I mean, I get it,
> don't tag for the data consumer.  But on the other hand, don't break the
> data consumer with stupid tagging schemes, either.
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