[OSM-talk] Complex turn restrictions

[Claudius]

Am 24.04.2009 07:19, Paul Johnson:
> 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)?

That's a real tough one, but I think it cannot be resolved with current 
restrictions alone. It would need some to-be-made-up lane restrictions. 
[1] includes some first thoughts about lanes, while [2] already talks 
about lane-specific restrictions.

Claudius

[1] http://wiki.openstreetmap.org/wiki/Relations/Proposed/Lane
[2] http://wiki.openstreetmap.org/wiki/Proposed_features/lane_and_lane_group