[OSM-talk] ref in roundabouts

[Simon Hewison]

On Tue, 2008-10-07 at 11:45 +0200, Celso González wrote:
> Two options here:
> -ref is the one or ones that are used in the highway
> -ref is not needed at all
> 

I'd suggest that ref is not needed at all, unless the roundabout itself
has one that is unique to itself. Quite often roundabouts are named. I
guess that some of them may have some official reference number as well.
It shouldn't normally have either name, or reference of any of the
joining ways.

Any route describing software should pick up on junction=roundabout, and
work out which exit of the roundabout to describe the manoeuvre as, and
ideally what the signposts might say on that exit.

Of course, counting exits needs to count permitted exits - quite often
some roundabouts have oneway roads joining them, if they're not leading
away from the roundabout, you don't count them.

Some examples of roundabouts that might cause problems:

The Handy Cross Interchange, High Wycombe:
http://www.openstreetmap.org/?lat=51.61291&lon=-0.76999&zoom=16&layers=B000FTF

A4 Wellington Street/A412 junction in Slough:
Note: This is not grade-separated. Traffic going along the A4 is allowed
to go straight over the top of the roundabout. The ways across the top
of the roundabout are indeed part of the A4.

http://www.openstreetmap.org/?lat=51.50815&lon=-0.581066&zoom=18&layers=B000FTF

Then of course, there's got to be the obligatory roundabout with
oneway=false. This one is the Magic Roundabout at Hemel Hempstead, but
there are others. At the moment, this one isn't labelled as
junction=roundabout.

http://www.openstreetmap.org/?lat=51.746358&lon=-0.47329&zoom=18&layers=B000FTT

-- 
Simon Hewison