Technological change and the concentration of the US general cargo port system: 1970-88

Using the Gini coefficient, we show that general cargo port traffic has become more concentrated from 1970 to 1988 because of four technological changes: containerization, larger ships, larger trains, and computerisation of freight tracking and billing. These four technological changes have spawned four kinds of intermodal services: microbridge, minibridge, landbridge, and round-the-world. Anticipated future technological innovations are expected to continue the concentration trend. In a methodological note, we show how the Gini coefficient will tend to underestimate system concentration in longitudinal studies of contracting systems, and we introduce a simple step that may be taken to avoid this error. -from Authors