Railroad Track Modernization Act of 2003

Railroad Track Modernization Act of 2003 - Amends federal rail transportation law to replace the Secretary of Transportation's discretionary program of grants to states for light density rail line pilot projects with a mandatory program of capital grants for railroad track.

Directs the Secretary to establish a program of capital grants to class II and class III railroads (or, with the concurrence of such a railroad, to a state or local government) to rehabilitate, preserve, or improve railroad track (including roadbed, bridges, and related track structures) used primarily for freight transportation. Requires rehabilitation, preservation, or improvement to a standard ensuring that the track can be operated safely and efficiently and accommodate 286,000 pound rail cars.

Sets forth certain employee protection and prevailing wage requirements with respect to grant projects.

Directs the Secretary to study and report to Congress on such projects to determine the public interest benefits associated with the light density railroad networks in the states and their contribution to a multimodal transportation system.