The Safeguarding Transit Operations to Prohibit China Act, or STOP China Act, seeks to mitigate national security risks by restricting the use of federal funds for vehicles and vehicle technologies from certain foreign entities. Congress asserts that the People's Republic of China (PRC) uses industrial policies to gain market dominance and that PRC-developed technologies pose significant national security threats, undermining U.S. competitiveness and supply chains. The bill amends existing law and introduces new prohibitions, defining a "covered entity" as one based in, controlled by, or otherwise linked to a "covered nation" (as defined in 10 U.S.C. 4872(d), which includes China, Russia, Iran, and North Korea). It prohibits the use of federal funding, including both Chapter 53 funds and other Department of Transportation appropriations, for contracts to procure "covered vehicles" or for infrastructure to fuel or charge such vehicles. A covered vehicle is defined as rolling stock produced by a covered entity or incorporating an electric power train from a covered entity. The United States Trade Representative, in consultation with the Attorney General and the Secretary of Transportation, is mandated to create and regularly update a public list of these prohibited covered entities. Exceptions to the prohibition are made for vehicles or infrastructure used for inspection, investigation, or motor vehicle safety research, development, or testing. The act also includes a severability clause to ensure that if any provision is deemed invalid, the remainder of the act remains in effect.