The pipeline industry has approximately 100 companies, as compared to the motor carrier industry, with more than 50,000.

1) What are the underlying economic causes for this difference, given the fact that they both carry approximately the same volume of intercity tone-miles?

2) Water carriers played a dominant role in the transportation system of the United States in the 18th and 19th centuries. Why has their relative position declined during the 20th century? Are they still an important component of the total transportation system? why? or why not?