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