The aim is globally, we're working on speeding it up and cleaning out trains and water... We'll probably finish the US within a few days and move on to the EU or other places.
Can imagine train traces particularly being tricky. Might have to build a separate routing graph of just train lines and filter out any traces that match that too strongly - though I don't think people mapping train lines in OSM work too hard to get train lines' routeability right...
