Bridge Investment Act This bill establishes a bridge investment program to provide financial assistance for projects to repair, improve, rehabilitate, or replace a bridge on a public road. The program includes small, medium, and large bridge projects and nationally or regionally significant projects involving more than $500 million. The program's goals include improving the safety, efficiency, and reliability of the movement of people and freight over bridges and the reduction of the number of bridges in need of significant repair. The Department of Transportation may award grants for bridge investment projects that meet specified criteria. The Government Accountability Office shall conduct, and report on, an assessment of the bridge investment grant program.