Abstract
The measurement of returns to scale in transport industries has become increasingly sophisticated. In this paper, attempts to increase the understanding of returns to scale in transport industries by examining the relationship between firm size and the characteristics of the output that firms produce are made. It is argued that output characteristics are positively correlated with, and influenced by, firm size. As a result, when firm size increases, output characteristics also change in a direction that reduces unit costs. Drawing on evidence from the US trucking industry, an appropriate specification indicates that economies of scale may well exist in the US trucking industry. (Author/publisher).