[Tagging] Bridges and layers

[Liz]

On Wed, 28 Jul 2010, Anthony wrote:
> > That's not sufficient. You'd have to do some kind of heuristic test to
> > see whether they were approximately parallel as well
> 
> You said they were parallel.  Twice in fact.

but not all dual carriageways are parallel so the heuristics have to cover 
that possibility as well
example
http://www.openstreetmap.org/?lat=-34.7699&lon=148.812&zoom=14&layers=M