[OSM-newbies] Bridges over canals - ref=**

[Nick Allen]

Hi,

I've been working on a section of canal in the UK, and have been adding
bridges etc. I've researched the wiki thoroughly and as far as I can see
bridge numbers (traditional way of knowing where you are on a canal),
should be tagged using the ref=**.  

This is fine, but where a classified road crosses the canal two
references result. This link shows the A426 crossing bridge 58 over the
Oxford canal;
http://www.openstreetmap.org/?lat=52.389392&lon=-1.254384&zoom=18&layers=B000FTF

As you can see, Mapnik has rendered this to show both references.

If I'm getting the tagging right, will this cause problems for routing
software for car drivers in the future  ... 'Follow the A426 for 12
miles then cross bridge 58'.  Could make the M6 more interesting as I
believe it crosses several canals.

Am I getting this wrong, or;
a/ does mapnik need an update, or
b/ does an additional tag need to be used?

Tallguy
(aka Nick)