Opened 9 years ago

Last modified 8 years ago

#3567 new enhancement

Add ability to create a no_u_turn restriction with a way "via"

Reported by: ponzu Owned by: potlatch-dev@…
Priority: major Milestone:
Component: potlatch2 Version:
Keywords: Cc:


Potlatch2 currently has a dialog for creating a no_u_turn restriction with a node as the "via" member. As more and more divided roads are being (correctly) split into to one-way ways, the intersections are represented by either one or four short ways instead of a node. Creating a no_u_turn restriction for such intersections with a way as the "via" member currently involves a lot of clicks. The UI could works as follows:

  1. Split ways at intersection as needed.
  2. Click the intended "from", "via" and "to" ways in order.
  3. Select Transport->No U Turn
  4. Go into the UI to adjust/enhance the relation thus created.

Change History (5)

comment:1 Changed 9 years ago by Richard

We'll certainly add this, but probably not before P2 goes live on the main site (as we're concentrating on bugfixes and parity with P1 for now), and with a UI that's consistent with the existing editor rather than the above "click in order" idea.

comment:2 Changed 9 years ago by stevage

Can you point us to an example of this kind of intersection somewhere? I'm having trouble picturing it.

comment:3 Changed 9 years ago by ponzu

Certainly: There are no U turns allowed at the intersection of Enterprise and Parker Place. Therefore, four turn_restriction relations are required. Because both Enterprise and Parker Place are drawn as divided roads, it is meaningless to used the nodes as the "via" members. The routing algorithms will ignore such restrictions because they will consider each maneuver in question to be a left turn onto the cross-street rather than a U turn. At the same time, it will not do to add left turn restrictions, because left turns are, of course, permitted. I was told in the Help forum that using the short section of the cross street as the "via" member does the trick and the routing algorithms respect it. I personally have not had a chance to verify this theory because CloudMade? takes forever to accommodate the OSM changes and this particular intersection still looks as it was 2 weeks ago before I added the restrictions. But I assume the person who gave this advice knows what he is talking about. Now if only it was as easy to create such restrictions as it is to create them when the "via" member is a node.

Here's the original discussion:

comment:4 Changed 9 years ago by stevage

Thanks for the concrete example. I'm not sure what the "ultimate" GUI behaviour for this would be, but this would work:

If there are exactly three ways selected, and if they connect end to end, and if at least one is oneway=yes/-1, then we can unambiguously determine the three roles.

It would be nice to have proper editors for the different kinds of turn restrictions, and a way to add ways to a relation (rather than only being able to add relations to a way).

comment:5 Changed 8 years ago by L. David Baron

A simpler example, where the ways involved are not all oneway, is the intersection of 20th and Guerrero in San Francisco.

There are signs facing both directions forbidding U-turns on Guerrero (i.e., from Guerrero and to Guerrero), which is divided. 20th is not divided.

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