The federal agency that regulates pipeline maintenance is ___________.

The Pipeline and Hazardous Materials Safety Administration (PHMSA) is the federal agency responsible for ensuring the safe transportation of energy and hazardous materials by pipeline. PHMSA establishes regulations and offers guidance on pipeline maintenance, construction, and operation to protect the public and the environment. This includes overseeing safety standards for pipeline systems and enforcing compliance through inspections and enforcement actions.

Other agencies, while they play vital roles in environmental protection, worker safety, and regulatory oversight, do not specifically focus on pipeline maintenance. For example, the Environmental Protection Agency (EPA) mainly addresses environmental issues, the Nuclear Regulatory Commission (NRC) focuses on nuclear energy and materials safety, and the Occupational Safety and Health Administration (OSHA) is concerned with workplace safety across various industries. Therefore, PHMSA's dedicated mission to pipeline safety and maintenance distinguishes it as the correct answer.