Validate turn restrictions with to = from

[naoliv]

Could JOSM validate turn restrictions where to is the same way/node as from?

[mdk]

what about restriction=no_u_turn?

[skyper]

So far only roles are checked.

Think validator could check for incorrect turn restrictions like:

1. except `restriction=no_u_turn´:
   • from and to need to be different ways
2. for from and to ways, via node:
   • via needs to be end node of from and to
     • if from is tagged oneway=yes, via needs to be last node of from (except restriction:[mode] exists and from is tagged oneway:[mode]=no)
     • if to is tagged oneway=yes, via needs to be first node of to (except restriction:[mode] exists and to is tagged oneway:[mode]=no)
3. for all members ways:
   • all ways need to be connected at end nodes
     • if a way is tagged oneway=yes, it needs to point from from to to (except restriction:[mode] exists and the way is tagged oneway:[mode]=no)

And we could even check for the right access tags on all ways.

[mdk]

And keep in mind, that via also could be a way.

[naoliv]

What I see that is wrong (ie, JOSM should give a warning):

1) we have a no_u_turn in a street that ends somewhere (without any kind of key/value in the last node); if it's forbidden to make an U-turn then it makes the street a dead-end (the vehicle can enter the street but will never be able to get back)
2) likewise, but with a highway=turning_circle
3) likewise, but with a noexit=yes
4) we have a no_u_turn in the middle of the street, forbidding a U-turn at the junction/crossing; this should be considered forbidden by default (making this no_u_turn unnecessary), otherwise we will have one no_u_turn restriction for every highway crossing in the map.
5) having a no_u_turn in highway=footway makes no sense (a person walking on it can't go back?)
6) likewise, but with highway=path
7) to, via and from are all the same section of highway; it's just wrong and JOSM should warn.

What could be valid (and JOSM should not warn):

8) a no_u_turn using a highway=mini_roundabout as via
9) a no_u_turn using one or more ways/nodes as via

The example OSM file is attached.

[naoliv]

A no_u_turn using a via node with traffic_calming=island could also be valid (and should not trigger a warning).

[skyper]

Think this test was implemented some time ago and there a warnings about unconnected members under Role verification problem like The "from" way does not start or end at a "via" node.