Following a discussion with jburgess and artem on IRC, I started fixing up Leipzig's trams where a single way has two railway and highway tags (instead of two ways reusing the same nodes). Apart from maintaing these ways (i.e., does a maxspeed tag also apply to the tram? Probably not!), it was also causing rendering issues in Mapnik (see https://trac.mapnik.org/ticket/66).

I started with all the secondary roads, and it seems to have worked well (I kept an original OSM file of the area just in case). The ways with highway=secondary retain all the other tags which might be on there, while the ways with the railway=tram tag have just this and possibly a bridge tag.

The procedure was taking the OSM file and treat it with some Emacs keyboard macros and search and replace etc. (to assign negative ids to the new ways), and with JOSMs search feature.

If the renderers are happy, I will repeat the process with the other highway types in the next few days.

Comments welcome.