Yes; 1/25th the
area. "Size" is ambiguous. A car might be 5m long, but what's its
volume?
Some statistics:
From
here and
here.
So it seems that as area increases, the roads that are in that area (in the real world)
tend to increase in length roughly as to the power of 1/√2. That's either scarily coincidental, or we've stumbled upon something scary about the universe!
Anyway, it would imply that a generated road, like those in the real world, made in an area 1/25th the size would tend to only be 1/10th the length.
It also implies we could get realistic road networks up to about 550 km total length from 400 km²; if PD are working on generating road networks and not just single loops and point-to-point, then that'd be incredible.
But then, those are average figures (contrast with the high density in Ronda), and a game isn't bound by the tedium of reality, either. The above numbers may even be total rubbish, probably, but basically the decrease in area isn't as catastrophic at it might seem, especially given we probably weren't going to make best use of the larger area in the first place...