[Talk-us] Check your turn:lanes

Paul Johnson baloo at ursamundi.org
Thu Aug 25 17:57:35 UTC 2016

On Thu, Aug 25, 2016 at 12:42 PM, Toby Murray <toby.murray at gmail.com> wrote:

> On Thu, Aug 25, 2016 at 12:09 PM, Jack Burke <burkejf3 at gmail.com> wrote:
> > So I take it that at least you and I are in agreement that the wiki is
> > deficient for branching exits like this one:
> > http://mapillary.com/map/im/7igAGXSa6EsUYlTIujXchw
> Why does this example even need any special lane tagging? I would map
> this as lanes=3 on the motorway and then draw the motorway_link with a
> lanes=1 tag out to right in front of where that picture is.

Because what's obvious to a human isn't going to be obvious to a machine.
Let's try a similar but slightly more complicated example with no lane
markings but definite turn lanes:


Right now the section leading up to the junction is tagged
"slight_left|slight_left;through|through", with the left junction being
"junction:ref=2" "destination=Glenpool;Okmulgee" and "destination:ref=US 75
South"; the right route is "destination=Oklahoma City", "destination:ref=I
244 West".   The turn lane part is technically correct, but the ground
perspective makes it look almost the opposite; I'm considering changing the
"through|through" part to "slight_right|slight_right" for clarity
(especially given that almost all traffic exits I 244 for Exit 2 towards
Okmulgee here).  Osmand invents four lanes without the lane tagging, which
doesn't help if you're still behind the curve and don't know the setup at
the decision point.

> Right now
> the motorway_link doesn't branch off of the main way until WAY past
> where the white solid line starts and where you must commit to the
> exit.

I would put the motorway_junction node at the commit point (the start of
the theoretical gore).  Extending the ramp lane centerline tends to be
messy and cause routers to assume you've already left the freeway before
you've even made the turn on particularly wide motorways.  Obviously I'm
not actually looking at the data to see what it is right now.
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