It depends... If the route is based on an actual DEM and there are existing maps, I would then place the roads, or at least some of them, in the proper place. If not I would place them where they would make sense, and even build up small clusters of homes and industries along the way.
For TIGER images to load up in TANE you need to install the HOG textures. I believe most are built-in now, but there maybe some missing. It's been awhile since I've used those myself since I've moved on to TransDEM, which by the way has the proper textures for TANE and they work flawlessly.
John