[OSRM-talk] Sharp Turns Onto Ramps

Bryce Jasmer bryce at jasmer.com
Mon Sep 4 20:31:34 UTC 2017


I saw Daniel <http://www.openstreetmap.org/user/daniel-j-h>'s diary entry
</> several weeks ago when it was included in the weekly OSM email and was
very intrigued with the project. The ideas behind his work seemed solid and
a real problem was pointed out that could be fixed to improve things.

However, I'm a little bit confused on what the recommended solution is to
these "sharp turns". The diary entry didn't call them out explicitly, and
the Goff Mountain example in the diary remains unchanged as of yet. For
Goff Mountain, are you supposed to click on the node intersection at the
"second ramp" and change the green arrow allowing a near-u-turn to red so
that routing software won't try to send the user into a potentially illegal
or dangerous maneuver?

That was my assumption on the proper fix, so I went ahead and made a couple
of hundred changes in my state. After I was complete with my state, I
noticed that many of my changes were being reverted or overwritten and the
turn restrictions removed. I asked the user why they were undoing my
changes and they rightly pointed out Relation:restriction
<http://wiki.openstreetmap.org/wiki/Relation:restriction> wiki page which
states "*Don't map * turn restrictions that are *the default* for a given
jurisdiction *and* are *not signed*. It is much better to ensure that
routing engines embody the regional rule rather than mapping every
occurrence as a turn restriction." They suggested instead to use some turn
lane plugins for JOSM, but after reading up on those, they seemed
incredibly complex and require a lot more work than simply saying "you
can't turn right on that ramp" with a couple of clicks in iD. It is also
very difficult to tell from satellite images just how many lanes exist for
some of these places, so it makes mapping properly with lane designations
impossible to do remotely and would require field work and will likely mean
the end of this clean-up.

So I turn to this list to find out what the right approach is. Is the
recommendation to not add turn restrictions to an intersection as the wiki
states since they are not signed? Is it to work with the JOSM plug-ins to
do the more labor intensive mapping and splitting and counting of lanes and
their individual restrictions?

At this point I'm stuck on what is right. Please help.

Thanks,
b-jazz
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