Lately I've been experimenting using Sketchup, then exporting as a Collada (.dae) and using ModelConverterX's ground polygon wizard.
I lay out a rectangle of photoscenery on Sketchup (with proper dimensions) and use that as my reference to draw things out. I create a master file, then export one .dae file for the pavement, one for the detail textures, one for the markings, etc. then merge all the files into one using MCX's "merge" prompt. When you compile that merged file using MCX's groundpoly wizard, make sure you assign each material the right layer to prevent z-fighting.