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                                                                     EXHIBIT 4.3

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                          SECOND SUPPLEMENTAL INDENTURE

                           DATED AS OF MARCH 16, 1999

                                       TO

                                    INDENTURE

                           DATED AS OF APRIL 10, 1992

                       -----------------------------------

                                     BETWEEN

                              GREYHOUND LINES, INC.

                                       AND

                 STATE STREET BANK AND TRUST COMPANY, AS TRUSTEE

                       -----------------------------------

                8-1/2% CONVERTIBLE DEBENTURES DUE MARCH 31, 2007

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         SECOND SUPPLEMENTAL INDENTURE, dated as of March 16, 1999 (this "Second
Supplemental Indenture"), between GREYHOUND LINES, INC., a Delaware corporation
(the "Company"), and STATE STREET BANK AND TRUST COMPANY, as trustee (the
"Trustee").

         WHEREAS, the Company and the Trustee (as successor to Shawmut Bank
Connecticut, N.A., formerly The Connecticut National Bank) entered into an
Indenture, dated as of April 10, 1992 as supplemented by the First Supplemental
Indenture dated as of December 22, 1994 (the "Indenture"), pursuant to which the
Company issued its 8-1/2% Convertible Subordinated Debentures due March 31, 2007
(the "Debentures"); and

         WHEREAS, pursuant to Section 1301 of the Indenture, Holders of the
Debentures presently have the right prior to Maturity to convert any Debenture
or Debentures into shares of Common Stock of the Company at the rate of 80.81
shares of Common Stock for each $1,000 principal amount of Debentures; and

         WHEREAS, pursuant to Section 1306 of the Indenture, in the case of any
merger of another person into the Company, the Debentures will be convertible
only into the kind and amount of securities, cash and other property receivable
in such merger by a holder of the number of shares of Common Stock of the
Company into which such Debentures might have been converted immediately prior
to such merger; and

         WHEREAS, the Company, Laidlaw Inc., a Canadian corporation ("Laidlaw")
and Laidlaw Transit Acquisition Corp., a Delaware corporation and a wholly owned
subsidiary of Laidlaw ("Acquisition") have entered into the Amended and Restated
Agreement and Plan of Merger, dated as of November 5, 1998 (the "Merger
Agreement"), pursuant to which Acquisition will be merged with and into the
Company, with the Company being the surviving corporation ("Merger"); and

         WHEREAS, upon completion of the Merger, each share of Common Stock of
the Company will be converted into the right to receive $6.50 in cash; and

         WHEREAS, the Merger was completed on March 16, 1999; and

         WHEREAS, to establish the conversion rights of a Holder of Debentures
following the Merger and in accordance with Section 1306 of the Indenture, the
Company has agreed to execute and deliver this Second Supplemental Indenture;
and

         WHEREAS, the Company has complied with all the conditions and
requirements necessary under the Indenture to effect this Second Supplemental
Indenture, and the execution and delivery of this Second Supplemental Indenture
has been duly authorized in all respects by the Company;

         NOW, THEREFORE, in consideration of the above premises, the Company and
the Trustee agree, for the benefit of the other and for the equal and ratable
benefit of the Holders of the Debentures, as follows:

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                                   ARTICLE I

                             AMENDMENT OF INDENTURE

         Section 1.01  Amendment.  The Indenture is hereby amended as follows:

                  (a)      Notwithstanding anything to the contrary contained in
the Indenture, including Article Thirteen thereof, from and after the date of
this Second Supplemental Indenture, a Holder of any Debenture or Debentures
shall have the right to receive, upon conversion of such Debenture or Debentures
in accordance with the Indenture, an amount in cash equal to $525.27 for each
$1,000 principal amount of Debentures so converted.

                                   ARTICLE II

                            MISCELLANEOUS PROVISIONS

         Section 2.01 Terms Defined. For all purposes of this Second
Supplemental Indenture, except as otherwise defined or unless the context
otherwise requires, terms used in capitalized form in this Second Supplemental
Indenture and defined in the Indenture have the meanings specified in the
Indenture.

         Section 2.02 Indenture. Except as amended by this Second Supplemental
Indenture, the Indenture and the Debentures are in all respects ratified and
confirmed and all the terms shall remain in full force and effect. The Trustee
has no responsibility for correctness of the recitals of facts herein contained
which shall be taken as the statements of the Company, and makes no
representations as to the validity or sufficiency of this Second Supplemental
Indenture and shall incur no liability or responsibility in respect of the
validity thereof.

         Section 2.03 Governing Law. THIS SECOND SUPPLEMENTAL INDENTURE SHALL BE
GOVERNED BY AND CONSTRUED IN ACCORDANCE WITH THE LAWS OF THE STATE OF NEW YORK,
AS APPLIED TO CONTRACTS MADE AND PERFORMED WITHIN THE STATE OF NEW YORK, WITHOUT
REGARD TO PRINCIPLES OF CONFLICT OF LAWS.

         Section 2.04 Successors. All agreements of the Company in this Second
Supplemental Indenture shall bind it successors. All agreements of the Trustee
in this Second Supplemental Indenture shall bind its successors.

         Section 2.05 Multiple Counterparts. The parties may sign multiple
counterparts of this Second Supplemental Indenture. Each signed counterpart
shall be deemed an original, but all of them together represent the same
agreement.

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                                   SIGNATURES

         IT WITNESS WHEREOF, the parties hereto have caused this Second
Supplemental Indenture to be duly executed as of the date first written above.

                                             GREYHOUND LINES, INC.

                                             /s/ Craig R. Lentzsch
                                             -----------------------------
ATTEST:                                      Craig R. Lentzsch, President and
                                             Chief Executive Officer

/s/ Mark E. Southerst
-------------------------------------
Mark E. Southerst, Vice President and
General Counsel and Secretary

                                             STATE STREET BANK AND TRUST
                                             COMPANY, as Trustee

                                             By: /s/ Susan C. Merker
                                             -----------------------------------
ATTEST:                                      Name: Susan C. Merker
                                             Title: Vice President

By: /s/ Elizabeth C. Hammer
    ----------------------------------
Name: Elizabeth C. Hammer
Title: Vice President