Mosaic terrtex at Watts, with Paint Shop Pro. I just spent about two hours or so on an experiment around the Watts car house. I settled on a good image file from Textures.com for painting roadbeds around the yard and right of ways at the junctions. The image is
TexturesCom_SoilBeach0100_1_seamless_S.jpg which I rotated 90 degrees and darkened in Paint Shop Pro. I then selected the areas to work on with the "lasso" freehand tool and cloned parts of the image over the selected areas on the extracted terrtex files. Afterwards I went into the route editor and deleted all the pesky transfers, and voila! I also cloned-in some dried grass textures bordering the right of ways, and some lawns around the west side of the area.
I have found sand images the best for making a gravel like texture, it translates very well and this shade of color complements the track textures Malte is using quite nicely.