[Tagging] Cycle boxes for two-stage left turns

[Jarek Piórkowski]

On Wed, 8 Jan 2020 at 08:03, marc marc <marc_marc_irc at hotmail.com> wrote:
> Le 08.01.20 à 05:10, Marc Gemis a écrit :
> > On Tue, Jan 7, 2020 at 10:30 PM marc marc <marc_marc_irc at hotmail.com> wrote:
> >> keep it simple !
> >> advanced stop box only use a cycleway=asl without relation
> >> https://wiki.openstreetmap.org/wiki/Tag:cycleway%3Dasl
> >> a single node is not enought ?
> >
> > The problem I see with this approach is that the node has to be placed
> > on the other street than the one the cyclist is using.
>
> I don't think so.
> we must do the same as for a traffic sign stop :
> add the node to the affected way with cycleway=tsb or any other value
> with the same meaning.

Thanks for the suggestion!

Looks like this should work for symbolic meaning (with some refinement
like cycleway:forward=tsb probably, and perhaps a fully spelled-out
value since the acronym is not really established). However it seems a
bit problematic geometrically: unlike with a stop sign where we can
place the node on where the OSM way crosses the stop line (or a very
short extension thereof), here the node needs to be a couple of meters
away from the actual box, and not really in a geometrically meaningful
position. As far as I can tell the tag cannot be on the intersection
node itself as I can't see a way to reliably indicate which of the
crossing ways has a turn box. See example at
https://bin.piorkowski.ca/2020/osm_cycleway_tsb_on_node.png (note is
only explanatory here)

Routers would then have to look for a cycleway=tsb node shortly before
a possible left turn. Would this be preferable from an algorithm's
point of view to looking for a relation?

Thanks!
--Jarek