I’m using this trick only for the highest zoomlevels. The lower the zoom, the thinner the roads, and on those levels it isnt too much of a problem. The only problem I still have is that I also want to indicate bike routes on top. This is not possible unless I make ‘window’ holes in the 0x10106 bitmap. Disadvantage of those holes is that the roads on my latest map still shows a bit more spaghetti effect. See for an example http://sites.google.com/site/openfietsmap/news/22-04-2011