Final answer:
The Department of Transportation (DOT) is responsible for regulating interstate shipments of hazardous materials.
Step-by-step explanation:
The federal agency responsible for regulating interstate shipments of hazardous materials is the Department of Transportation (D).
This agency's regulations encompass not just the transport of these materials, but also their safety protocols, handling procedures, and emergency response in case of accidents or spills.
While other agencies like the Environmental Protection Agency (EPA) also play a role in the oversight and management of hazardous materials, particularly related to hazardous waste, it is the Department of Transportation that is specifically tasked with the regulation of their transportation.