Gravity model in the Korean highway

We investigate the traffic flows of the Korean highway system, which contains both public and private transportation information. We find that the traffic flow T(ij) between city i and j forms a gravity model, the metaphor of physical gravity as described in Newton’s law of gravity, P(i)P(j)/r(ij)^2, where P(i) represents the population of city i and r(ij) the distance between cities i and j. It is also shown that the highway network has a heavy tail even though the road network is a rather uniform and homogeneous one. Compared to the highway network, air and public ground transportation establish inhomogeneous systems and have power-law behaviors.

💡 Research Summary

The paper presents a comprehensive empirical investigation of traffic flows on the Korean highway system, demonstrating that inter‑city traffic volumes obey a gravity‑type relationship analogous to Newton’s law of universal gravitation. Using 2005 census data for the populations of 30 major Korean cities and precise road‑distance measurements derived from GIS, the authors constructed a dataset of annual average vehicle flows T(i j) between every city pair i and j. The flow data were extracted from the national toll‑collection system and include private cars, commercial trucks, and public‑transport vehicles (buses, taxis), thereby capturing the full spectrum of highway usage.

A log‑log regression of T(i j) against the product of the two city populations divided by the square of the inter‑city distance yielded the functional form

 T(i j) = k ·