Who is the US DOT? And what is their role?

The US Department of Transportation (DOT) oversees all United States transportation matters via Airline, Highway, Rail and Ocean and even Pipeline transportation.

In terms of dangerous goods safety, the Pipeline and Hazardous Materials Safety Administration oversees and publishes the Hazardous Materials Regulations (HMR) found in the Code of Federal Regulations, Title 49 (49-CFR).