Yeah I've seen pictures of the motorway thing, seems pretty handy especially when like you say there are 4 lanes or whatever.
I was thinking of something more for urban areas though, with traffic lights and that, although as Pete says, a map view might be more helpful there, unless some kind of virtual scene could be constructed akin to the motorway one. (are they generated automatically, or are they pre-rendered?)
I think someone should do a system using augmented reality where it uses a HUD on your windscreen and overlays an arrow on the junction it wants you to turn off on, now that would be cool!