The Jones act restricts ship traffic between US ports solely to US-flagged vessels dramatically reducing competition and increasing costs, and you move freight by ship across a continent with rivers and canals
This doesn't stop nearly as many people/companies as much as I wish it would.
This prevents someone from say dropping off all their goods in Miami, then letting a British liner pick them up later and drop half off in NYC, and the other half in London.
Instead you have to either ship it yourself to NYC and Miami, or you have to send it by train to NYC from Miami.