[Tagging] Tunnels and bridges

[Malcolm Herring]

On 31/01/2013 12:37, Martin Koppenhoefer wrote:
> drawing the outline seems a good approach as it permits to group
> visually (and topologically) different carriageways running over the
> same bridge (as opposed to two parallel bridges).

This is approach is used by IHO for marine chart data. Where a bridge 
has more than span, they further divide the bridge outline into two or 
more butted polygons, one for each span, so that each span can have its 
own height & width attributes. They also map bridge piers as separate 
objects.