[OSM-talk] Complex turn restrictions

[Aun Johnsen (via Webmail)]

On Thu, 23 Apr 2009 22:19:39 -0700, Paul Johnson <baloo at ursamundi.org>
wrote:
> In Salem, Oregon, I have encountered a ramp that I can't quite seem to
> make a restriction that JOSM thinks is valid, so I'm wondering what the
> expected way to handle such a situation is.  The area in question is
> visible at
>
http://www.openstreetmap.org/?lat=44.929397&lon=-123.024784&zoom=18&layers=B000FTF
> 
> Coming from the flyover ramp to Mission Street eastbound, as well as
> from the Mission Street bike lane ramp where that lane rejoins the road,
> drivers and cyclists alike are faced with a No Lane Change line that
> prevents a legal movement to the left turn lanes onto 17th Street.
> Effectively, this means that you may or may not be able to turn left at
> 17th depending on how you entered from the next intersections west.  You
> can see the pavement markings as they are on the ground at
>
http://maps.google.com/?ie=UTF8&ll=44.92934,-123.02527&spn=0.000872,0.002414&t=k&z=19
> 
> For those who aren't familiar with why this is a hard question:
> 
> 1) JOSM doesn't seem to want to have more than one "via" or have a way
> as a "via" in a restriction relation; I'm not sure if this is right or
> wrong for JOSM to expect.  What's the live use on this?
> 
> 2) Solid white lane lines mean you can't change lanes in this area
> (exception being bicycles are allowed to enter or leave their restricted
> lane over the solid line adjacent to the bicycle restricted lane).
> 
> 3) Only one lane change is allowed per vehicle per 1000 feet.  Lane
> changes are unrestricted between all lanes for 60 feet between the two
> intersections, and traffic moves at expressway speeds (40-50MPH).
> 
> So how does one handle such awkward turn restrictions (other than
> slaughtering the civil engineer who came up with such a bogus
> interchange to begin with)?
This is not a turn restriction, as you are allowed to turn left from the
road, but rather a lane change restriction. This must be handled in the map
somehow as well, but there is no way to tag it at the moment to my
knowledge. I suggest somebody start working on a lane relation, as much
information lies in lanes, such as specified lanes for left and right turn,
off-ramps, where you can change lane, where you cannot change lane,
differented restrictions in different lanes (such as you cannot change
between the left-most lanes where an onramp comes on right-hand side of a
motorway, restrictions applying only for one movement, not the other (i.e.
you can change lane to the left, but not to the right). I am more than
willing to help you form such a relation, but doesn't have time to do the
work myself.
-- 
Brgds
Aun Johnsen
via Webmail