Which government agency primarily regulates the transportation of hazardous materials by road?

HAZMAT REGULATORY FRAMEWORK involves multiple federal agencies with different but overlapping jurisdictions: PHMSA (Pipeline and Hazardous Materials Safety Administration): Part of the DOT; issues the Hazardous Materials Regulations (HMR) in 49 CFR Parts 100-185; sets standards for classification, packaging, marking, labeling, placarding, and documentation; develops and updates the Hazardous Materials Table; FMCSA (Federal Motor Carrier Safety Administration): Also part of DOT; enforces HazMat regulations on motor carriers through roadside inspections and carrier audits; issues the CDL regulations requiring HazMat endorsement and knowledge test; the CDL Manual Chapter 9 is the primary study resource because FMCSA administers the endorsement; TSA (Transportation Security Administration): Administers the security threat assessment for HazMat endorsement; specifically added after 9/11 concerns about hazmat trucks as potential weapons; EPA: Regulates hazardous waste (under RCRA) which overlaps with DOT when hazardous waste is being transported — dual compliance required; OSHA: Worker safety during loading/unloading; does not regulate transport itself but overlaps during facility operations. DRIVER COMPLIANCE STANDARD: CDL drivers transporting hazmat must comply with BOTH the FMCSA regulations (from a motor carrier/driver perspective) AND the PHMSA hazardous materials regulations (from a cargo handling/labeling/documentation perspective).