  Because of increasing global urbanization and its immediate consequences,
including changes in patterns of food demand, circulation and land use, the
next century will witness a major increase in the extent of paved roads built
worldwide. To model the effects of this increase, it is crucial to understand
whether possible self-organized patterns are inherent in the global road
network structure. Here, we use the largest updated database comprising all
major roads on Earth, together with global urban and cropland inventories, to
suggest that road length distributions within croplands are indistinguishable
from urban ones, once rescaled to account for the difference in mean road
length. Such similarity extends to road length distributions within urban or
agricultural domains of given area. We find two distinct regimes for the
scaling of the mean road length with the associated area, holding in general at
small and at large values of the latter. In suitably large urban and cropland
domains, we find that mean and total road lengths increase linearly with their
domain area, differently from earlier suggestions. Scaling regimes suggest that
simple and universal mechanisms regulate urban and cropland road expansion at
the global scale. As such, our findings bear implications for global road
infrastructure growth based on land-use change and for planning policies
sustaining urban expansions.
