The Department of Transportation works with DHS agencies to secure what?

The correct answer highlights the Department of Transportation's collaboration with agencies of the Department of Homeland Security to secure the nation's ports. Ports represent critical infrastructure for both economic activity and national security, handling the import and export of goods and facilitating international trade. Given their strategic importance, securing ports includes protecting against terrorism, ensuring the safe passage of cargo, and managing risks associated with maritime transportation.

In this context, while the nation's airspace, roads, and railways are also important aspects of national transportation infrastructure and security, the explicit joint efforts of the Department of Transportation and DHS are particularly emphasized in relation to ports. This collaboration focuses on enhancing security measures and protocols to safeguard these vital entry points against potential threats and vulnerabilities.