What is the proper way to add "No U Turn" restrictions when the way is split?
**Summary**: I don't see the intuitively correct way of creating "No U turn" restriction relationships on intersections where one or both roads are represented by parallel one-way ways. Is there one?
**Detailed **UPDATE**
I have deleted most of my original post. I realize that my problem statement**
I think the current rules (and editing capabilities was not with the schema for turn restrictions, but with the way it is implemented in Potlatch) Potlatch 2. Due to the way Potlatch 2 "simple" mode allows one to easily create no-u-turn restrictions with a via node, it did not even occur to me that via could be a way.
So really my question now becomes: is there a "simple" way to create a no-u-turn restriction in Potlatch 2 where via member is a way?
Here is what I do now:
1. Split ways inside the intersection as needed.
2. Ctrl-click (Command-click on Mac) one side of the road, the short section of the cross road to the left of it and the reverse side of the road.
3. Add all three to a new relationship.
4. Set relationship to Advanced->Turn restriction.
5. Set type to No U turns.
6. Click Members and set roles: to, via and from (have to type).
Can this be simplified at all? Is this a wishlist for adding "No U Turns" restrictions were written with the single two-way road intersections in mind. So maybe I should stop splitting major roads in my areas into two one-way roads, because I am having a heck of a time adding U turn restrictions. First off, let me ask why we're adding these restrictions. They don't show up on the generated maps (most of them anyway). I assume it's for routing.
Consider a situation where a split way intersects a split way. I am not good with ASCII art, so picture this. Street A running North to South and Street B running East to West. This creates four intersection nodes. Call them, counterclockwise from bottom right, ANBE (for A Northbound intersecting B Eastbound), ANBW, ASBW and ASBE.
Let's say A Northbound (AN) has a "No U turn" restriction at the intersection. I could split AN at ANBE, call the south section AN1 and say "no U turn at ANBE from AN1 to AN1". This may or may not be relevant. Since BE is one-way, going right, the routing algorithm may already know not to allow either left or U turn an ANBE.
I could further split AN at ANBW, calling the small segment between ANBE and ANBW AN2. I could then say "no U turn an ANBW from AN2 to AN2". Fine, but because there is a small segment of BW between ANBW and ASBW, the routing algorithm is likely to consider it a left turn, not a U turn. I cannot place a "no left turn" restriction, because the left turn is very much allowed.
What is the solution? Has it been tested on routing algorithms and apps or are we just saying "we can only do so much creating data, it's up to the other folks to interpret it properly"?Potlatch?
