The NTSB is an independent agency responsible for investigating transportation accidents, including aviation, highway, marine, pipeline, and rail accidents. The NTSB does not have regulatory or enforcement authority, but its recommendations are often adopted by government agencies and industry stakeholders.

The FAA is an independent agency within the U.S. Department of Transportation responsible for regulating the safety of civil aviation. The FAA sets and enforces safety standards for aircraft, airports, and air traffic control, and it investigates aviation accidents and incidents.

The PHMSA is an independent agency within the U.S. Department of Transportation responsible for regulating the safety of pipelines and hazardous materials transportation. The PHMSA sets and enforces safety standards for pipelines and hazardous materials, investigates pipeline and hazardous materials accidents, and provides training and technical assistance on pipeline and hazardous materials safety.

The FRA is an independent agency within the U.S. Department of Transportation responsible for regulating the safety of railroads. The FRA sets and enforces safety standards for railroads, investigates railroad accidents and incidents, and provides training and technical assistance on railroad safety.

The NHTSA is an independent agency within the U.S. Department of Transportation responsible for regulating the safety of motor vehicles and highways. The NHTSA sets and enforces safety standards for motor vehicles, investigates motor vehicle accidents, provides funding for highway safety programs, and conducts research on highway safety.

The USCG is an independent agency within the U.S. Department of Homeland Security responsible for regulating the safety of maritime transportation. The USCG sets and enforces safety standards for vessels, investigates maritime accidents and incidents, and provides training and technical assistance on maritime safety.

The TSA is an independent agency within the U.S. Department of Homeland Security responsible for preventing terrorism and other threats to transportation systems. The TSA screens passengers and baggage at airports, seaports, and other transportation hubs, and it conducts security assessments of transportation systems and infrastructure.

The FTA is an independent agency within the U.S. Department of Transportation responsible for regulating the safety of public transportation systems. The FTA sets and enforces safety standards for public transportation vehicles and infrastructure, investigates public transportation accidents and incidents, and provides training and technical assistance on public transportation safety.

The STB is an independent agency responsible for regulating the economic aspects of surface transportation, including railroads, motor carriers, and pipelines. The STB does not have a direct role in transportation safety, but its regulations can have an impact on safety by affecting the financial health and operating practices of transportation providers.

The FMCSA is an independent agency within the U.S. Department of Transportation responsible for regulating the safety of commercial motor vehicles. The FMCSA sets and enforces safety standards for commercial motor vehicles and drivers, investigates commercial motor vehicle accidents and incidents, and provides training and technical assistance on commercial motor vehicle safety.

The RITA is an independent agency within the U.S. Department of Transportation responsible for conducting research on transportation safety, developing and deploying innovative transportation technologies, and providing training and technical assistance on transportation safety. The RITA's research and development efforts are aimed at improving the safety of all modes of transportation.

The FRA is an independent agency within the U.S. Department of Transportation responsible for regulating the safety of passenger rail transportation. The FRA sets and enforces safety standards for passenger rail vehicles and infrastructure, investigates passenger rail accidents and incidents, and provides training and technical assistance on passenger rail safety.

The MARAD is an independent agency within the U.S. Department of Transportation responsible for promoting the development of the U.S. maritime industry, regulating the safety of maritime transportation, and providing financial assistance to the U.S. maritime industry. The MARAD's safety regulations cover a wide range of topics, including vessel design, construction, and operation.

The PHMSA is an independent agency within the U.S. Department of Transportation responsible for regulating the safety of pipelines. The PHMSA sets and enforces safety standards for pipelines, investigates pipeline accidents and incidents, and provides training and technical assistance on pipeline safety.

The FHWA is an independent agency within the U.S. Department of Transportation responsible for regulating the safety of highways and bridges, providing funding for highway construction and maintenance, and conducting research on highway safety. The FHWA's safety regulations cover a wide range of topics, including road design, construction, and maintenance.