I’d have a couple concerns with that approach, starting with the degradation of the foam placed on the ground. After the bugs / whatever ate it away (e.g., see related posts on bridges & portals), you’d be left with a thin concrete shell. Even if the foam survived, stepping on it would crush that and the concrete veneer.
Maybe I’m missing the benefit of “light weight”? Are you intending portability? If so, I’d doubt the foam would be rigid enough to extract a road section from the dirt and relocate intact. Then there’s all the curves and intersections which the 2nd locale wouldn’t match.
Consider also the perfectly-even trench that would have to support the foam, to prevent it and its veneer from breaking.
So, why not just concrete, or something similar but stronger? The benefits of that include being able to lay it into an uneven shallow trench, push some mesh in, and smooth out the surface. It would follow the curves and slopes, and permit any type and angle of intersection, all without sawing foam or making perfect trenches.
All you’d need to do is play in the dirt and make some roads! Which can be lots of fun!!
My two cents,