Dangerous Goods and Haz-Mat: Pretty much mean what they describe in their names.
On-land, and in this country; Controls are heavily regulated by both Federal and States. Regulations are also backed up in State Regulations; which will, generally, mirror what the Federal Codes specify.
Each State has enforcement agencies that monitor the flows of commercial traffic, for not only trucking, but also railroads, as well. The enforcement issues for trucking are failrly evendent; as one travels about the country…
The enforcement personnel for railroads, work mostly out of sight of the public, checking mostly, paperwork, and in areas away from view of the regular public. Enforcement personnel, are employed by many different official branches of the States. From Highway Patrols, to Officers of the various Secretaries of State Enforcement personnel, to Business Liscensing Agencies of States, Local Police Departments and Sheriff’s Offices may also field Enforcement Agents, as well.
Enforcement of water-born carriage is mostly, done by agents of/ and for, the U.S. Coast Guard, who will board vessels to check out compliance issues.
Railroad containers being shipped by rail, in this country are required to disaplay, their speciffic, designated placcards; placed on all sides of the container, similarly, to the placement of placcards on rail carload shipments (either for a returning empty car, and surely, for the loaded portion of the trip.)