Which of the following defines the restrictions imposed on non-US flagged vessels?

The restriction imposed on non-US flagged vessels is that they cannot carry goods between US ports. This is due to the Jones Act, a federal law that stipulates that only vessels that are built in the United States, owned by US citizens, and crewed by US citizens or permanent residents may transport goods between US ports. This regulation is designed to promote domestic shipping and protect the American maritime industry. As a result, non-US flagged vessels are effectively barred from engaging in cabotage, which refers to the transportation of goods between ports within the same country. This restriction is a key factor in maintaining a strong US merchant marine presence.

The other options do not accurately reflect the specific restrictions on non-US flagged vessels. For instance, while non-US flagged vessels can engage in international trade, the significant limitation is their inability to transport goods between US ports. Additionally, while there may be certain customs duties associated with foreign vessels, the greater impact is the cabotage rule rather than higher duties specifically. Lastly, stating that they are allowed to operate only on US routes is misleading because, while they can operate in US waters under certain conditions, the crucial restriction is their prohibition from carrying goods between US ports.