  This paper shows that a well designed transport system has an embedded
exchange value by serving as a market for potential exchange between consumers.
Under suitable conditions, one can improve the welfare of consumers in the
system simply by allowing some exchange of goods between consumers during
transportation without incurring additional transportation costs. We propose an
explicit valuation formula to measure this exchange value for a given
compatible transport system. This value is always nonnegative and bounded from
above. Criteria based on transport structures, preferences and prices are
provided to determine the existence of a positive exchange value. Finally, we
study a new optimal transport problem with an objective taking into account of
both transportation cost and exchange value.
