I take it you are looking at making your own path and road. I would not get to concerned at getting the measurements exact, I am sure that there is no set standard as to how wide a path should be. As to roads, I also don't think these would be made to a set width. remember, most roads at that period had not been laid specifically for the motor vehicle.
Try and find some pics of the region you want your dio set in with something in it that you know the size of, a tank for example.
I am a Norfolk man and i glory in being so
On the bench: Airfix 1/72nd Harrier GR.3/Fujimi 1/72nd Ju 87D-3