[OSM-talk] Crossing ways

[David Earl]

On 11/08/2007 15:21, Jon Bright wrote:
> Hi,
> 
> Now that I've found the validation panel in JOSM, I have a question 
> about crossing ways.
> 
> I have a dual carriageway, which has a junction with a minor road. 
> Traffic on the minor road can join the dual carriageway in either 
> direction.  Traffic on either part of the dual carriageway can join the 
> minor road.  Traffic on the dual carriageway cannot perform a U-turn.
> 
> I'd tried to represent this with the ways in the screenshot at
> 
> http://discord.ensued.net/crossingways1.png
> 
> The validator complains that the selected ways cross one another.  There 
> are no bridges or tunnels involved here - the whole thing's controlled 
> with traffic lights.  My question is, what to do in this situation:
> 
> - Should I have organised the junction differently?
> - Should I just ignore the validator's warning?
> - Should I put set one of the ways as layer=1, even though they're not 
> really above one another?
> - Something else I didn't think of?

Here's the typical way to do it.

                   |
     --------------x------------
                   |
     --------------x------------
                   |
                   |

(where x are nodes)

Among numerous examples, see:
http://www.openstreetmap.org/?lat=52.20926889478002&lon=0.1425119753953168&zoom=18&layers=B0F

Note that Godesdone Road does not have a way through onto the westbound 
carriageway: there is a solid reservation there; River Lane and Coldhams 
Lane do connect across the reservation. (One could argue that the 
highway style for the linking bit of Colhams Lane should be primary, not 
secondary I guess).

(Linear) ways should only cross without a node if there is a bridge or 
tunnel, and then they should be in separate layers.

How to represent permitted turning movements at a junction is an ongoing 
discussion. It needs relationships between ways and/or segments which we 
don't have yet. There have been a number of proposals for this; 
Frederick is working on something now.

David