Rendering highway lanes

Why does not Mapnik render highway lanes? There is a great inconsistency about what [highway=trunk][1] means... sometimes it is used for single lane roads (mostly in United Kingdom) and sometimes it is used for say 2nd grade motorways (multiple lanes, continental western Europe for instance). If we rendered highway lanes, this inconsistency would disappear. [1]: http://wiki.openstreetmap.org/wiki/Tag:highway%3Dtrunk