Which level of government holds fundamental legal authority for most roads and public transportation in the U.S.?

The fundamental legal authority for most roads and public transportation in the U.S. resides primarily with state governments. This is due to the structure of government in the United States, where states have the constitutional responsibility for establishing and maintaining transportation systems within their borders. States possess the authority to enact laws, create policies, and allocate funding for infrastructure projects, including highways and public transit systems. This level of government is key in the planning, construction, and maintenance of roadways, making decisions that directly impact transportation efficiency and safety.

Federal involvement in transportation typically includes funding and support through grants and regulations, but the actual control and operation of roads mainly lie within state jurisdiction. Local government and municipal authorities may manage roadways and public transport within their communities, but they operate under the broader authority set by the state.