I have extracted all the turn_restriction that exist in the planet OSM file
In total there are around 500.000 in the OSM Database
2% of them, or around 10.000 relations are broken, most of them because of other people that had added/ modified streets and deleted parts of the restriction relation.
A turn restriction is made of a TO - VIA - FROM relation
That means that the relation should be of 3 different elements.
Found over 1000 relations that have a turn restriction relation made of at least 4 members, and going up to 100 members, when the absolute value is a 3 members relation
I have found 9700 turn_restriction relations that are invalid, because users deleted part of the relations, either in editors like ID that does not work people that they will break a relation, or other possibilities
You can see one example here http://www.openstreetmap.org/relation/1110481/history
I had made a editable Google SpreadSheet where you can see all of the 10000 broken relations, you can download them and report the ones that you had fixed
Comment from SimonPoole on 29 December 2015 at 16:07
Funneling the information in to maproulette would probably make more sense (or in to osmose)
Comment from Arlas on 29 December 2015 at 16:15
you can send them to OSM restriction validator, it would allow other users to help fixing. http://restrictions.morbz.de/
Comment from Thomas8122 on 29 December 2015 at 16:18
A no_exit restriction can have more than 1 to member
A no_entry restriction can have more than 1 from member
no_u_turn: One (1) or more via ways
Comment from Sanderd17 on 29 December 2015 at 17:15
baditaflorin: a turn restriction can have more than 3 members. At least, it’s possible to have multiple “via” members.
However, that type of turn restriction doesn’t happen often in real life (it usually easier to set up physical barriers than signing the turn restriction), so I do think that most of your results are wrong, but there will be some correct turn restrictions there.
Comment from ika-chan! UK-USA on 29 December 2015 at 17:33
One of the problem behind this is that iD does not display turn restrictions very well. That is why so many new editors unwittingly break turn restrictions.
Comment from Richard on 29 December 2015 at 17:37
@Amaroussi: would you like to provide a citation for your blanket statement? iD’s turn restriction editor is excellent IMO.
Comment from baditaflorin on 29 December 2015 at 17:55
I did a random sample of 5 relations.
The user did not do a complete relation from the start http://www.openstreetmap.org/relation/5186076/history
The same user that did the relation, ended up broking it
User using ID broken the relation
User using JOSM broken this relation, and possbily more ( thare are 16 relation in this changeset http://www.openstreetmap.org/changeset/35613882
I now see that the number that i did can be as low as 6000, because in the process of using osmconvert and osmfilter , somewhere there it did not give me the nodes, so i have in my relations just the ways.
So a No_u_turn made up of a node and a way, i will count only once
As i have found in this false poziitive no_u_turn restriction http://www.openstreetmap.org/relation/4071659
Comment from ika-chan! UK-USA on 29 December 2015 at 18:58
@Richard, the restrictions do show in the sidebar it does not usually show up on the main editing screen (maybe I am just so used to JOSM, and I am a bit cranky for other reasons today).
Comment from Zartbitter on 29 December 2015 at 22:14
You can visualize the turn restrictions on my “map of turn restrictions” http://map.comlu.com/
Turn restrictions with (subjective) warnings and errors are marked. It tells you what is wrong with some broken restrictions.
Comment from BushmanK on 29 December 2015 at 22:15
@Richard, iD’s turn restriction editor is an excellent tool for its purpose.
But it doesn’t serve (and, probably, shouldn’t) as a warning, that will tell people anything about relations they can break unintentionally.
I have full HD resolution display. And here is how iD looks when I’ve picked a point, which has “via” role in two restrictions:
See anything about relations? Me neither. One should scroll the sidebar down to see at least small section with “All relations” title. And, because there is a tendency to hide “very complex” concept of relations from the newbies, there is a huge chance, that one of them will just disregard that section as “something out of his scope of simply editing the map”.
Comment from PlaneMad on 30 December 2015 at 05:05
It will be worthwhile to investigate to root cause of so many broken relations and how to reduce more breakage in the future. Working with relations definitely require a higher level of skill than other data types.
Its great to know there are QA tools like http://map.comlu.com/ and http://restrictions.morbz.de/ which help detect and fix them. The only problem is that it took me a random glance into the diary to find this out and I suspect most editors don’t even know that such tools exist. It would be great if all important tools like these were somehow accessible directly from osm.org for more visibility.
Comment from MarkusHD on 2 January 2016 at 10:44
https://wiki.openstreetmap.org/wiki/Quality_assurance lists them all, but you still have to be aware about it or find that site.