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Exhibit 4.6 FIRST WAIVER AND AMENDMENT TO THE CREDIT AGREEMENT FIRST WAIVER, dated as of April 18, 2005 (the Waiver and Amendment), under the
Amended and Restated Credit Agreement, dated as of June 24, 2004, (as amended, supplemented or
otherwise modified from time to time, the Credit Agreement), among TFM, S.A. DE C.V., a
corporation with variable capital (sociedad anonima de capital variable) organized under the laws
of the United Mexican States, (the Borrower), the several Banks parties thereto, and
JPMorgan Chase Bank, N.A. (f/k/a JPMorgan Chase Bank), as Administrative Agent. W I T N E S S E T H: WHEREAS, the Borrower, the Banks and the Administrative Agent are parties to the Credit
Agreement; and WHEREAS, the Borrower has advised the Banks that it intends to issue a minimum of $460,000,000
of senior notes (the New Notes), the proceeds of which will be used (i) to acquire the
Borrowers outstanding Senior Discount Debentures pursuant to a tender offer commenced on April 1,
2005, (ii) to pay accrued and unpaid interest thereon, (iii) to pay the fees of the underwriter
associated with the issuance of the New Notes and the tender offer, (iv) to pay the premium related
to the tender offer and (v) to pay other expenses, including legal fees, not to exceed $2,000,000
relating to the tender offer and the issuance of the New Notes (collectively, the Permitted
Purposes); and WHEREAS, the Borrower has further requested that the Credit Agreement be amended to allow it
to borrow up to $25,000,000 from Kansas City Southern (as successor in interest by merger to Kansas
City Southern Industries, Inc., KCSI) on a fully subordinated basis (the Subordinated
Intercompany Debt); and WHEREAS, the Borrower has requested the Banks (i) permit the issuance of the New Notes
notwithstanding the provisions of Section 6.9(b)(i) of the Credit
Agreement which limit the amount
of New Notes to an amount equal to or less than the principal amount of the Senior Discount
Debentures being refinanced and (ii) amend the Credit Agreement to permit the Borrower to issue the
Subordinated Intercompany Debt; and WHEREAS, the Banks are willing to agree to such waiver and amendment, but only upon the terms
and subject to the conditions set forth herein; NOW THEREFORE, in consideration of the premises and the mutual covenants hereinafter set
forth, the parties hereto hereby agree as follows: SECTION 1. Defined Terms. Unless otherwise defined herein, capitalized terms that are
defined in the Credit Agreement are used herein as therein defined. SECTION 2. Waiver to Credit Agreement. The Lenders hereby agree to waive, effective as of the
Effective Date, any Default or Event of Default under Section 7.1(c) of the Credit Agreement that
would otherwise result from the issuance of New Notes having a principal




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2 amount in excess of the principal amount of the Senior Discount -Debentures being refinanced,
provided that any proceeds of the New Notes not used for the Permitted Purposes shall be promptly
used to prepay the Term Loans, with any such prepayment being applied pro rata to theTranches of the Term Loans and to installments of principal due in each Tranche in the inverse
order of their maturity. SECTION 3. Amendment to Credit Agreement. Section 6.9 of the Credit Agreement is
hereby amended by (a) deleting the word and at the end of the clause (g) thereof, (b)
re-lettering clause (h) as clause (i); and (c) adding the following new clause (h) thereto: (h) up to $25,000,000 of Indebtedness to KCSI which (i) provides for no amortization
prior to to September 17, 2007, (ii) provides for no cash payments of interest while the
Loans are outstanding and (iii) is otherwise subordinated to the Loans on terms and
conditions reasonably acceptable to the Administrative Agent; and. SECTION 4. Conditions to Effectiveness. This Waiver and Amendment shall become
effective upon the date (the Effective Date) when the following conditions are satisfied: (a) Waiver and Amendment. The Administrative Agent shall have received counterparts
of this Waiver and Amendment, duly executed and delivered by the Borrower and the Majority Banks; (b) No Default. No Default or Event of Default shall have occurred and be continuing
on such date after giving effect to the waiver and amendments contained herein; and (c) Representations and Warranties. Each of the representations and warranties made
by the Borrower in or pursuant to the Credit Agreement shall be true and correct in all material
respects on and as of the date hereof after giving effect to this Waiver and Amendment, as if made
on and as of the date hereof, except to the extent such representations and warranties expressly
relate to a specific earlier date, in which case such representations and warranties were true and
correct as of such earlier date. SECTION 5. Continuing Effect of the Credit Agreement. This Waiver and Amendment shall
not constitute an amendment or waiver of any provision of the Credit Agreement not expressly
referred to herein and shall not be construed as an amendment, waiver or consent to any further or
future action on the part of the Borrower that would require an amendment, waiver or consent of the
Banks or Administrative Agent. Except as expressly amended or waived hereby, the provisions of
the Credit Agreement are and shall remain in full force and effect. SECTION 6. Counterparts. This Waiver and Amendment may be executed by one or more of
the parties hereto on any number of separate counterparts (including by facsimile), and all of said
counterparts taken together shall be deemed to constitute one and the same instrument. SECTION 7. Severability. Any provision of this Waiver and Amendment which is prohibited or unenforceable in any
jurisdiction shall, as to such jurisdiction, be ineffective to the extent of such prohibition or
unenforceability without invalidating the remaining provisions




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3 hereof, and any such prohibition or
unenforceability in any jurisdiction shall not invalidate or render unenforceable such provision in
any other jurisdiction. SECTION 8. Integration. This Waiver and Amendment and the Credit Agreement represent
the agreement of the Borrower, the Administrative Agent and the Banks with respect to the subject
matter hereof, and there are no promises, undertakings, representations or warranties by the
Administrative Agent or any Bank relative to the subject matter hereof not expressly set forth or
referred to herein or in the Credit Agreement. SECTION 9. GOVERNING LAW. THIS WAIVER AND AMENDMENT AND THE RIGHTS AND OBLIGATIONS
OF THE PARTIES UNDER THIS WAIVER AND AMENDMENT SHALL BE GOVERNED BY, AND CONSTRUED AND INTERPRETED
IN ACCORDANCE WITH, THE LAW OF THE STATE OF NEW YORK. THE PROVISIONS OF SECTIONS 9.13, 9.14 AND
9.16 OF THE CREDIT AGREEMENT SHALL APPLY MUTATIS MUTANDIS TO THIS WAIVER AND
AMENDMENT AS IF SET FORTH IN FULL HEREIN. [THE REMAINDER OF THIS PAGE IS INTENTIONALLY LEFT BLANK]




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IN WITNESS WHEREOF, the parties hereto have caused this Waiver and Amendment to be duly
executed and delivered by their proper and duly authorized officers as of the day and year first
above written. TFM, S.A. DE C.V.By:

/s/
Leon OrtizName:
    Leon OrtizTitle:
    Treasurer




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JPMORGAN CHASE BANK,
as Administrative AgentBy:

/s/
Leah E. HughesName:
    Leah E. HughesTitle:
    Authorized SignatoryJPMORGAN CHASE BANK,
as a BankBy:

/s/
Linda M. MeyerName:
    Linda M. MeyerTitle:
    Vice President




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BANK OF AMERICA, N.A.By:

/s/
Javier OrozcoName:
    Javier OrozcoTitle:
    Vice President




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COMERICA BANKBy:

/s/
Robert J. HurleyName:
    Robert J. HurleyTitle:
    Vice President




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HSH NORDBANK AGBy:

/s/
DolliName:
    DolliTitle:
    Vice President




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STANDARD CHARTERED BANKBy:

/s/
Fernando IglesiaName:
    Fernando IglesiaTitle:
    Senior Vice President




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BBVA BANCOMER S.A.By:

/s/
Leonardo F. Sanchez EspejelName:
    Leonardo F. Sanchez EspejelTitle:
    Director Divisional II Banca CorporativaBy:

/s/
Jvan A. Vazquez ChabollaName:
    Jvan A. Vazquez ChabollaTitle:
    Director Divisional II Banca Corporativa




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BANCO NACIONAL DE MEXICO, S.A.,INTEGRANTE DEL GRUPO
FINANCIERO BANAMEXBy:

/s/
Antonio Muñoz GómezName:
    Antonio Muñoz GómezTitle:
    DirectorBy:

/s/
Federico Delgada PastorName:
    Federico Delgada PastorTitle:
    Director




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EXPORT DEVELOPMENT CANADABy:

/s/
IllegibleName:Title:  By:

/s/
IllegibleName:Title:




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WESTLB AG, NEW YORK BRANCHBy:

/s/
Stephan KloockName:
    Stephan KloockTitle:
    Regional HeadBy:

/s/
Daniel HitchcockName:
    Daniel HitchcockTitle:
    Executive Director