when we invented turn restrictions back in the ages it seems we made a mistake.
When we named the restrictions we gave the mappers the impression that geometry matters for turn restrictions. So mappers think from the naming that “no_left_turn” is something different than “no_right_turn” - But it isnt.
In routing we simply assume a “no_*” means we cant traverse from the from edge via the via vertex to the to edge. We dont process geometry. So even if the mapper ment to restrict a left_turn them might actually have restricted a right turn just by selecting a wrong way.
Its the same for all the “only_*” type of restrictions. So in the end it would have been much better to just name them “no” and “only” or something.
This causes some confusion in mappers when i tell them that their turn restriction broke something as it didnt do what it says.
Its nice that at least Josm shows the icons for the restriction though.
While I generally agree that this can be tricky, I don’t think there’s a big problem with the naming of the restrictions.
First, “only_right”, “no_left” etc is how they are called and signed on the streets, so mappers would probably expect to add them exactly like it is currently used.
Including the direction is valuable information, because surely being able to find cases where problems might exist is still better than not at all being able to identify (without going there or using another resource) if the restriction is inconsistent/wrong?
if the restrictions have names we can show these specific icons, which wouldn’t be possible with just no and only, definitely not without looking at the geometry, as it is now.
But it does not include the direction - It shows a specific icon. Which direction the turn restriction establishes is only a matter of the referenced OSM object.
Thats the point - the icon shown and the restriction beeing implied can be totally different things and mappers wont notice unless looking at individual turn restrictions and which objects are in from/via/to.
Because of the low usage of turn restrictions only
I don’t really see an issue, if there are a lot of mistagged restrictions (type doesn’t fit the referenced geometry) then a suitably motivated person could write a OSMOSE test (not completely trivial but doable).
Osmose was reporting issues, regarding a banned left turn (exceptionally rare in Ireland as we drive on the left, unless the destination road is one-way). iD was indicating that there was no problem. However, on checking street-level imagery, the actual ban is on certain right turn traffic.
Interestingly, some of the approaches to the roundabout were pointed in the wrong direction (resulting in problems like in the image), which makes me wonder if there was a non-compliant change as some point in how the turn restrictions and one-ways were managed.
