Yes, of course the grass areas, don't go across the highways, but the system is set up so that the road automatically takes precedence. Hence the map looks correct when used. The road symbol is wider than the road on the ground, so any map derived from the OpenStreetMap will be practical.
I disagree with not joining the grass verge to the road centre, as any map derived from that data has a white space between the road and the grass, which clearly doesn't exist on the ground.