The impact of scale on energy intensity in freight transportation

• Modal energy intensity is mainly determined by scale.
• Data shows a tight energy intensity versus scale relationship for road, rail, air, and water modes.
• Reducing energy intensity through larger scale faces diminishing returns.

This paper analyzes energy intensities of ships, diesel–fuelled railways, trucks, and aircraft, using publicly available data. The analysis suggests that differences in operation, not technology, explain most of the variation in energy intensity within and across modes. Among the operational characteristics, most important is the amount of cargo weight transported per vehicle and therefore the scale of the respective transportation system. It is found that each mode has a characteristic envelope in an average energy intensity versus average cargo weight diagram, and estimates of the elasticities of energy intensity with respect to load size are made.