The Transportation Department oversees the safety and funding of America's transportation network, including highways, railroads, aviation, pipelines, and maritime shipping. It runs the Federal Aviation Administration, which controls U.S. airspace and certifies aircraft as safe to fly, and the National Highway Traffic Safety Administration, which sets vehicle safety standards and orders recalls.

The department distributes federal highway funding to states through the Federal Highway Administration, drawn primarily from the Highway Trust Fund, financed by federal gas taxes, and it oversees Amtrak, the federally supported national passenger rail system, along with major transit and infrastructure grant programs for cities and states.

Beyond funding and regulation, the department investigates transportation safety more broadly through coordination with the independent National Transportation Safety Board, and its decisions on issues like drone regulation, electric vehicle infrastructure, and self-driving car rules increasingly shape emerging transportation technologies.

Most of the department's money is a pass-through: it distributes highway, transit, and airport funds to states, cities, and airport authorities largely by formula, and its own workforce is concentrated in the FAA, which employs about three-quarters of all DOT staff. Other operating administrations cover pipelines and hazardous materials (PHMSA), commercial trucking and bus safety (FMCSA), and the Maritime Administration, which maintains a reserve merchant fleet.