Earl, download Galadriel's Mirror or Eldar House (in the freebies here at R'osity) and take a look at the terrain material - you can reverse-engineer it.  I draw paths, streambeds, etc. as RGB areas onto a black background to change the terrain from grass (black) to worn path (green) or muddy streambed (blue) or stony outcrop/ledge (red).

     It will look intimidating at first, but it is just repeated node assemblies - a cluster each for black, red, green, and blue.  There may also be what looks like a duplicated set of image maps.  They are actually a little different.  These serve to scramble the tiling so that when covering huge areas you avoid that checkerboard appearance.

     You would need to make your own RGB map to suit where you want a road on whatever terrain you're using,  and change the master scaling math node to re-scale for a different terrain.

Let's see...  this is a little path behind Eldar house.  Just draw the green squiggly line on the RGB map wider, and you make a road.  Draw a thin black line down the center of the wide green line to get a two-tracks effect.

     If you're not in a hurry, I'm in process of a very large Poser terrain playset, Lothlorien (MkIII), and it could easily accommodate a road with a horse-drawn carriage.  Hmmm... a stone/wood bridge wide enough for a horse drawn carriage would be a good optional prop for that playset.  If you are in a hurry, I could send you a beta of the Lothlorien playset.

Poser 12, in feet.  

OSes:  Win7Prox64, Win7Ultx64

Silo Pro 2.5.6 64bit, Vue Infinite 2014.7, Genetica 4.0 Studio, UV Mapper Pro, UV Layout Pro, PhotoImpact X3, GIF Animator 5