Rural Rail Infrastructure Act of 1993 - Amends the Department of Transportation Act to increase the FY 1994 authorization of appropriations for local rail freight assistance. Authorizes appropriations for such assistance for FY 1995 through 1997. Requires the Secretary of Transportation, in addition to other criteria used in considering applications for rail freight assistance, to give priority to projects which enhance safety, including projects which improve, rehabilitate, or reconstruct bridges. Amends the Railroad Revitalization and Regulatory Reform Act of 1976 to authorize specified amounts of loan guarantees for any fiscal year for railroad improvements. Revises repayment, prepayment penalty, and interest rate provisions with respect to such guarantees.