Damage from air pollution appears not to justify large reductions in automobile travel in typical US urban areas; but it does justify significant expenditure on control of pollution. But local conditions vary widely, and some categories of pollution were not covered
American inland waterway transport is subject to a complicated system of control by government agencies, which require knowledge of costs. Inland waterway costs have fallen slightly, and a large share of the market has come into the hands of a small number of firms. The authors find increasing returns to scale for size of firm and output.
The road damage externality is much more important than the urban congestion problem in less developed countries, in sharp contrast to the experience of the developed countries. There is no justification for petrol taxes to exceed the taxes imposed on diesel fuel.
