This bill establishes a new competitive grant program to provide capital assistance for the maintenance, replacement, and rehabilitation of commuter rail bridges. The program authorizes the Secretary of Transportation to award grants to operators of public transportation systems for these critical infrastructure needs. A "commuter rail bridge" is defined broadly to include structures also used by intercity passenger rail, other public transportation, or roadways. Grants will be awarded through a competitive process, with the Secretary considering factors such as the applicant's system size, the bridge's age and condition, and whether the project is a priority in the applicant's transit asset management plan. Eligible costs are limited to the net capital costs attributable to public transportation use, and applicants must secure bridge access agreements if they do not own the bridge. The bill authorizes an appropriation of $1.5 billion annually for fiscal years 2027 through 2031 to fund this program.