It's been awhile for me so hopefully I can give you a few hints which others will assist you with.
You need a program called MicroDEM to manipulate the maps and topology.
https://www.usna.edu/Users/oceano/pguth/website/microdem/microdem.htm
You then need to obtain the TIGER map information. These I think are available from the National Geologic Survey as .shp (Shape files).
You put it all together and take the files from MicroDEM and run them through HOG, and the output produces and older version-Trainz route.
This is the gist of the process and there's probably a lot more to it than this.
If you are really, really interested in topographic maps and DEM files to produce routes, you may want to invest in TransDEM.
http://www.rolandziegler.de/StreckeUndLandschaft/startseiteTransDEMEngl.htm
While not free like MicroDEM - it's only about $32 USD or about 28 Euro or thereabouts - and it's well worth the investment. With TransDEM, you can place topomaps and Google Earth images directly on top of the imported DEM files right off their servers. Using the built-in tools allow you to trace your route, trim out unneeded baseboards, and export a Trainz route ready for work in Surveyor. There's even options to place track as well if you want to go that far.
There are other advantages as well including much higher accuracy. TIGER-generated maps from MicroDEM can be as far as 10 meters or more off regarding placement of the roads and other markings on the underlying DEM. This can cause rail lines to ride up hillsides and rivers to be far from their embankments. TransDEM is accurate enough to place topographic maps from the 1940s directly on DEM files generated today from Satellites and only be off a few meters.
There's a bit of a learning curve with this, but the documentation is well written and there is lots of developer and end-user support both on the TransDEM forums as well as here in these forums by the developer and users alike.
