Technological Change and the Concentration of the U.S. General Cargo Port System: 1970–88

Abstract

The diffusion of containerization has changed not only how general cargo is handled, but where. 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 computerization of freight tracking and billing. These four technological changes have spawned four kinds of intermodal services: microbridge, minibridge, landbridge, and round-the-world. We reconcile this concentration trend with Hayuth's (1988) seemingly contradictory finding that containerized cargo, which makes up most of general cargo, became less concentrated throughout the U.S. port system from 1970 to 1985. Anticipated future technological innovations are expected to continue the concentration trend. Our results fit well into Slack's (1990) proposed addition of a seventh stage (dropping of redundant nodes) to the Taaffe, Morrill, and Gould (1963) model of network development. 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.

Key words:

• containerization
• intermodal
• liner shipping
• ports
• concentration
• Gini coefficient
• technological change