# The scaling structure of the global road network

## TL;DR

This study reveals universal scaling patterns in the global road network, showing that road length distributions in urban and cropland areas are similar when scaled appropriately, and identifies two regimes governing road expansion.

## Contribution

It uncovers universal scaling laws in global road networks and distinguishes two regimes of road length growth with land area, informing infrastructure planning.

## Key findings

- Road length distributions in urban and cropland areas are statistically similar.
- Two distinct scaling regimes for mean road length with land area are identified.
- Mean and total road lengths increase linearly with domain area in large regions.

## Abstract

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.