American Infrastructure Investment Fund Act

American Infrastructure Investment Fund Act - Establishes the American Infrastructure Investment Fund in the Department of Transportation (DOT) to: (1) invest in infrastructure projects that increase or otherwise improve U.S. economic output, productivity, or competitive commercial advantage; (2) provide funding for projects that face significant funding barriers because of the need to combine resources across multiple jurisdictions or modes of transportation; and (3) improve the efficiency or throughput, the safety, and the environmental sustainability of a national or regional transportation network.

Requires the Fund to publish: (1) a detailed description of its strategy in an Investment Prospectus, and (2) its Operating Guidance for the Fund's management.

Requires the President to appoint the Fund's Executive Director, by and with the advice and consent of the Senate, as well as a Fund Advisory Committee.

Authorizes the Fund to provide direct loans and loan guarantees to eligible recipients for activities related to the planning, preparation, or design of an eligible project proposal.

Prohibits the use of funds for a project for the construction, alteration, maintenance, or repair of a public building or public work unless all of the iron and steel used in the project is domestic, except in certain circumstances.

Directs the Secretary of Transportation to establish: (1) a competitive national infrastructure investment grant program, and (2) an oversight program to monitor the effective and efficient use of funds authorized under this Act.

Sets forth the federal share of net project costs at 80%.