<PAGE>   1
                                                                    EXHIBIT 10.7

                       SECOND AMENDMENT TO SECOND AMENDED
                          AND RESTATED CREDIT AGREEMENT

     This SECOND AMENDMENT TO SECOND AMENDED AND RESTATED CREDIT AGREEMENT (this
"Amendment") is made and entered into effective as of January 31, 1999, by and
among DYNAMEX INC. (the "Borrower"), a Delaware corporation, DYNAMEX CANADA INC.
("Dynamex Canada"), a federal Canadian corporation, DYNAMEX OPERATIONS EAST,
INC. ("Dynamex East"), a Delaware corporation, DYNAMEX OPERATIONS WEST, INC.
("Dynamex West"), a Delaware corporation, ROAD RUNNER TRANSPORTATION, INC.
("Road Runner"), a Minnesota corporation, NEW YORK DOCUMENT EXCHANGE CORPORATION
("NYDEX"), a New York corporation, U.S.C. MANAGEMENT SYSTEMS, INC. ("USC"), a
New York corporation, DYNAMEX DEDICATED FLEET SERVICES, INC. ("Fleet Services"),
a Delaware corporation, CANNONBALL, INC. ("Cannonball"), an Illinois
corporation, NATIONSBANK, N.A. ("NationsBank"), a national banking association,
BANKBOSTON, N.A. ("BankBoston"), a national banking association, BANK AUSTRIA
CREDITANSTALT CORPORATE FINANCE, INC. (formerly Creditanstalt Corporate Finance,
Inc.) ("Creditanstalt"), a Delaware corporation, THE BANK OF NOVA SCOTIA
("Scotia Bank"), a Canadian banking association, BANK ONE, TEXAS, N.A. ("Bank
One"), a national banking association, NATIONSBANK, N.A. (formerly NationsBank
of Texas, N.A.), as agent for itself and the other Lenders (in such capacity,
together with its successors in such capacity, the "Agent") and BANKBOSTON, N.A.
and BANK AUSTRIA CREDITANSTALT CORPORATE FINANCE, INC. (formerly Creditanstalt
Corporate Finance, Inc.), as co-agents (the "Co-Agents").

                                    RECITALS:

     A. Pursuant to that certain Second Amended and Restated Credit Agreement
dated as of August 26, 1997, by and among the Borrower, Dynamex Canada, Dynamex
East, Dynamex West, Parcelway Courier Systems (B.C.) Ltd. (a British Columbia
corporation that has now been dissolved), Road Runner, NationsBank, BankBoston,
Creditanstalt-Bankverein, Scotia Bank, the Agent and BankBoston and
Creditanstalt-Bankverein as co-agents (as the same may be amended, renewed,
extended, restated or otherwise modified from time to time, the "Credit
Agreement"), the Lenders agreed to provide to the Borrower a senior secured
revolving credit and letter of credit facility (the "Credit Facility") in the
maximum aggregate principal amount of $75,000,000.

     B. Pursuant to that certain First Amendment to Second Amended and Restated
Credit Agreement dated as of May 5, 1998, the parties to the Credit Agreement
amended the Credit Agreement to increase the aggregate amount of the Credit
Facility to $115,000,000 and in certain other respects.

     C. The Borrower and its Subsidiaries, the Agent and the Lenders have
agreed, subject to the terms and conditions of this Amendment, to amend the
Credit Agreement to decrease the aggregate amount of the Credit Facility to
$65,000,000 and to amend the Credit Agreement in certain other respects.


<PAGE>   2


                                   AGREEMENTS:

     NOW, THEREFORE, in consideration of the premises and mutual covenants and
agreements contained herein and for other good and valuable consideration, the
receipt and sufficiency of which are hereby acknowledged, the parties hereto
hereby agree as follows:

     1. Terms Defined. Unless otherwise defined or stated in this Amendment,
each capitalized term used in this Amendment has the meaning given to such term
in the Credit Agreement (as amended by this Amendment).

     2. Amendments to Certain Definitions.

          (a) The following terms and definitions thereof set forth in Section
1.1 of the Credit Agreement are hereby amended and restated to read in their
entirety as follows:

          " 'Applicable Commitment Fee Rate' means, for the period commencing
     with the Closing Date and thereafter, the rate per annum set forth in the
     table below that corresponds to the ratio of (i) Funded Debt as of the date
     of the relevant financial statements referred to below to (ii) EBITDA for
     the four fiscal quarters of the Borrower and its Subsidiaries then most
     recently ended as of the date of such financial statements, calculated in
     accordance with Section 1.4:


<TABLE>
<CAPTION>
       Ratio of Applicable
      Funded Debt to EBITDA                   Commitment Fee Rate
      ---------------------                   -------------------
<S>                                           <C>
Less than 1.50 to 1.00                                       0.25%

Less than 2.00 to 1.00 but greater
than or equal to 1.50 to 1.00                                0.25%

Less than 2.75 to 1.00 but greater
than or equal to 2.00 to 1.00                                0.25%

Less than 3.00 to 1.00 but greater                           0.25%
than or equal to 2.75 to 1.00

Greater than or equal to 3.00 to 1.00                       0.375%
</TABLE>

     For purposes hereof and notwithstanding the preceding sentence, the
     Applicable Commitment Fee Rate for the period from the Closing Date to the
     first Calculation Date shall be deemed to be 0.25% and shall thereafter be
     calculated on each Calculation Date based upon the preceding table and the
     financial statements delivered by the Borrower pursuant to Section 8.1(b)
     and the certificate delivered by the Borrower pursuant to Section 8.1(d);
     provided, that the Applicable Commitment Fee Rate for the period from the
     Second Amendment Effective Date to the first Calculation Date thereafter
     shall be deemed to be 0.375%; provided further that if the Borrower fails
     to deliver to the Agent such financial statements or certificate on or
     before the relevant Calculation Date, the Applicable Commitment Fee Rate
     shall be deemed to be the percentage reflected in the preceding table as if
     the ratio of Funded Debt to EBITDA were greater than 3.00 to 1.00 until the
     date such statements and


<PAGE>   3
     certificate are received by the Agent, after which the Applicable
     Commitment Fee Rate shall be determined as otherwise provided herein."

          " 'Applicable Margin' means, for the period commencing with the
     Closing Date and thereafter, the rate per annum set forth in the table
     below that corresponds to the ratio of (i) Funded Debt as of the date of
     the relevant financial statements referred to below to (ii) EBITDA for the
     four fiscal quarters of the Borrower and its Subsidiaries then most
     recently ended as of the date of such financial statements, calculated in
     accordance with Section 1.4:


<TABLE>
<CAPTION>

                                                   Applicable Margins for
              Ratio of                       -----------------------------------
      Funded Debt to EBITDA                  ABR Loans          Eurodollar Loans
      ---------------------                  ---------          ----------------
<S>                                          <C>                <C>
Less than 1.50 to 1.00                              0%                      1.50%

Less than 2.00 to 1.00 but greater
than or equal to 1.50 to 1.00                       0%                      2.00%

Less than 2.75 to 1.00 but greater
than or equal to 2.00 to 1.00                    0.25%                      2.50%

Less than 3.00 to 1.00 but greater
than or equal to 2.75 to 1.00                    0.25%                      2.75%

Greater than or equal to 3.00 to 1.00            0.50%                      3.25%
</TABLE>

     For purposes hereof and notwithstanding the preceding sentence, the
     Applicable Margin for the period from the Closing Date to the first
     Calculation Date shall be deemed to be 0% for ABR Loans and 1.75% for
     Eurodollar Loans and shall thereafter be calculated on each Calculation
     Date based upon the preceding table and the financial statements delivered
     by the Borrower pursuant to Section 8.1(b) and the certificate delivered by
     the Borrower pursuant to Section 8.1(d); provided, that the Applicable
     Margin for the period from the Second Amendment Effective Date to the first
     Calculation Date thereafter shall be deemed to be 0.50% for ABR Loans and
     3.25% for Eurodollar Loans; provided further that if the Borrower fails to
     deliver to the Agent such financial statements or certificate on or before
     the relevant Calculation Date, the Applicable Margin shall be deemed to be
     the percentage reflected in the preceding table as if the ratio of Funded
     Debt to EBITDA were greater than 3.00 to 1.00 until the date such
     statements and certificate are received by the Agent, after which the
     Applicable Margin shall be determined as otherwise provided herein."

          "'Commitment' means, as to any Lender, the obligation of such Lender
     to make or continue Loans and incur or participate in Letter of Credit
     Liabilities hereunder in an aggregate principal amount at any one time
     outstanding up to but not exceeding the amount set forth opposite the name
     of such Lender on the signature pages hereto (or any amendment hereto)
     under the heading "Commitment" or, if such Lender is a party to an
     Assignment and Acceptance, the amount of the


<PAGE>   4


     "Commitment" set forth in the most recent Assignment and Acceptance of such
     Lender, as the same may be reduced or terminated pursuant to Section 2.12
     or 11.2, and "Commitments" means such obligations of all Lenders. As of the
     Second Amendment Effective Date, the aggregate principal amount of the
     Commitments is $65,000,000."

          "'EBITDA' means, for any period, without duplication, the sum of the
     following for the Borrower and its Subsidiaries (or other applicable
     Person) for such period determined on a consolidated basis in accordance
     with GAAP: (a) Net Income, plus (b) Interest Expense, plus (c) income and
     franchise taxes to the extent deducted in determining Net Income, plus (d)
     depreciation and amortization expense, plus (e) other non-cash items to the
     extent deducted in determining Net Income, including, for any calculations
     that include the fiscal quarter ended July 31, 1998, $1,573,000, and
     including, for any calculations that include the fiscal quarter ended
     January 31, 1999, $594,000, minus (f) non-cash income to the extent
     included in determining Net Income, plus (g) for any calculations that
     include the fiscal quarter ended January 31, 1999, $1,733,000."

          "'Lease Expense' means, for any period, the lease expense of the
     Borrower and its Subsidiaries for such period, determined on a consolidated
     basis in accordance with GAAP, and includes, without limitation, expenses
     under Operating Leases."

          (b) Section 1.1 of the Credit Agreement is hereby amended to add the
following new term and definition thereof, which term shall appear in
alphabetical order in such Section 1.1:

          "'Second Amendment Effective Date' means January 31, 1999."

     3. Amendment to Section 2.13. The first sentence of subsection (c) of
Section 2.13 of the Credit Agreement is hereby amended and restated to read in
its entirety as follows:

          "(c) The Borrower agrees to pay to the Agent for the account of each
     Lender, concurrently with the issuance of such Letter of Credit and on each
     Quarterly Date thereafter, a nonrefundable letter of credit fee with
     respect to each Letter of Credit issued in an amount equal to (i) the
     Applicable Margin for Eurodollar Loans, calculated in accordance with the
     definition of "Applicable Margin" contained herein, multiplied by (ii) the
     face amount of the Letter of Credit then in effect; provided, that the
     Applicable Margin for Eurodollar Loans for the period from the Second
     Amendment Effective Date to the first Calculation Date thereafter shall be
     deemed to be 3.25%."

     4. Amendment to Section 8.6. Section 8.6 of the Credit Agreement is hereby
amended to include a new fourth sentence, which sentence shall read in its
entirety as follows:


<PAGE>   5



     "Without limiting the generality of the foregoing, and notwithstanding
     anything to the contrary contained in this Section 8.6, the Agent or its
     representatives may, at the Borrower's expense, conduct a field exam during
     the period commencing with the Second Amendment Effective Date and ending
     on June 15, 1999."

     5. Addition of Section 8.18. The Credit Agreement is hereby amended to
include a new Section 8.18, which Section 8.18 shall read in its entirety as
follows:

          "Section 8.18 Limitation on Value of Alpine Enterprises, Ltd. The
     Borrower will ensure that Alpine Enterprises, Ltd. does not have assets
     valued at or exceeding Cdn.$1,500,000 at any time.

     6. Amendment to Section 9.3. The proviso at the end of Section 9.3 of the
Credit Agreement is hereby amended and restated to read in its entirety as
follows:

     "provided, however, that no Permitted Acquisitions may be made if (1) a
     Default exists at the time of such Permitted Acquisition or would result
     therefrom, or (2) the ratio of Total Debt to EBITDA for the most recent
     four fiscal quarters of the Borrower then ended, calculated in accordance
     with Section 10.1, is greater than 3.00 to 1.00 unless such Permitted
     Acquisition has been approved in writing by the Required Lenders."

     7. Amendment to Section 9.5. The proviso at the end of Section 9.5 of the
Credit Agreement is hereby amended and restated to read in its entirety as
follows:

     "provided, however, that (A) no Investments may be made by any Loan Party
     pursuant to clauses (g), (h), (i) or (j) preceding if a Default exists at
     the time of such Investment or would result therefrom and (B) no
     Investments in Alpine Enterprises, Ltd., other than amounts not to exceed
     Cdn.$250,000 in aggregate principal amount at any time outstanding loaned
     by Dynamex Canada to Alpine Enterprises, Ltd. pursuant to one or more
     intercompany notes, may be made by any Loan Party after the Second
     Amendment Effective Date."

     8. Amendment to Section 10.1. Section 10.1 of the Credit Agreement is
hereby amended and restated to read in its entirety as follows:

          "Section 10.1 Maximum Ratio of Total Debt to EBITDA. The Borrower and
     its consolidated Subsidiaries will not permit the ratio, calculated as of
     the end of each fiscal quarter of the Borrower commencing with the fiscal
     quarter ended April 30, 1997, and in accordance with Section 1.4, of (i)
     Total Debt to (ii) EBITDA for the four fiscal quarters of the Borrower then
     ended to be greater than the ratio set forth below for the applicable
     fiscal quarter end:


<PAGE>   6


<TABLE>
<CAPTION>
            Fiscal Quarter Ended                         Maximum Ratio
            --------------------                         -------------
<S>                                                      <C>
April 30, 1997, July 31, 1997, October 31, 1997,
January 31, 1998 and April 30, 1998                       3.25 to 1.00

July 31, 1998 and October 31, 1998                        3.00 to 1.00

January 31, 1999                                          3.25 to 1.00

April 30, 1999                                            3.50 to 1.00

July 31, 1999                                             3.75 to 1.00

October 31, 1999                                          3.60 to 1.00

January 31, 2000                                          3.10 to 1.00

April 30, 2000 and each fiscal quarter end                3.00 to 1.00"
thereafter
</TABLE>


     9. Amendment to Section 10.3. Section 10.3 of the Credit Agreement is
hereby amended and restated to read in its entirety as follows:

          "Section 10.3 Minimum Fixed Charge Coverage Ratio. The Borrower and
     its consolidated Subsidiaries will not permit the Fixed Charge Coverage
     Ratio, calculated as of the end of each fiscal quarter of the Borrower
     commencing with the fiscal quarter ended April 30, 1997, and in accordance
     with Section 1.4, for the four fiscal quarters of the Borrower then ended
     to be less than the ratio set forth below for the applicable fiscal quarter
     end:

<TABLE>
<CAPTION>
   Fiscal Quarter Ended                      Minimum Ratio
   --------------------                      -------------
<S>                                          <C>
 April 30, 1997, July 31,
 1997, October 31, 1997,
 January 31, 1998 and
 April 30, 1998                              1.50 to 1.00

 July 31, 1998, and October
 31, 1998                                    1.65 to 1.00

 January 31, 1999 and April
 30, 1999                                    1.00 to 1.00

 July 31, 1999                               1.25 to 1.00

 October 31, 1999 and
 each fiscal quarter end
 thereafter                                  1.50 to 1.00"
</TABLE>

     10. Amendment to Section 10.4. Section 10.4 of the Credit Agreement is
hereby amended and restated to read in its entirety as follows:


<PAGE>   7


          "Section 10.4 Capital Expenditures. The Borrower and its Subsidiaries
     (a) will not permit the aggregate Capital Expenditures of the Borrower and
     its Subsidiaries during the period from February 1, 1999 through and
     including January 31, 2000 (exclusive of any purchase or acquisition of
     Capital Stock or assets permitted by clause (ii) of Section 9.3) to exceed
     $3,500,000, and (b) will not permit the aggregate Capital Expenditures of
     the Borrower and its Subsidiaries during any period of four consecutive
     fiscal quarters (exclusive of any purchase or acquisition of Capital Stock
     or assets permitted by clause (ii) of Section 9.3) to exceed $3,500,000,
     provided, however, that the initial calculation with respect to this clause
     (b) shall be made as of April 30, 2000."

     11. Conditions Precedent. The effectiveness of this Amendment is subject to
the satisfaction of each of the following conditions precedent, all of which
conditions precedent must be satisfied on or before March 31, 1999:

          (a) The Agent shall have received all of the following, each dated
(where applicable and unless otherwise indicated) the date of this Amendment, in
form and substance satisfactory to the Agent:

               (i) Amendment Documents. This Amendment as executed by the
     parties hereto and any other agreement, document, instrument or certificate
     reasonably required by the Agent or the Lenders to be executed or delivered
     by the Borrower or any other Loan Party in connection with this Amendment,
     each duly executed by each of the parties thereto (collectively, the
     "Amendment Documents");

               (ii) Resolutions. Resolutions of the Board of Directors of the
     Borrower and the other Loan Parties certified by its Secretary or an
     Assistant Secretary which authorize the execution, delivery and performance
     by the Borrower and the other Loan Parties of this Amendment and the other
     Amendment Documents to which the Borrower or such Loan Party is or is to be
     a party;

               (iii) Legal Opinions. Legal opinions from Texas and Ontario
     counsel to the Borrower and its Subsidiaries;

               (iv) Amendment Fee. The amendment fee referred to in Paragraph 22
     of this Amendment;

               (v) Fees, Costs and Expenses. All fees, costs and expenses
     (including, without limitation, attorneys' fees and expenses) incurred by
     the Agent incident to this Amendment or required to be paid in accordance
     with Section 13.1 of the Credit Agreement, to the extent incurred and
     submitted to the Borrower, shall have been paid in full by the Borrower;
     and


<PAGE>   8


               (vi) Additional Information. The Agent shall have received such
     additional agreements, documents, instruments and information as the Agent
     or its legal counsel, Jenkens & Gilchrist, a Professional Corporation, may
     reasonably request to effect the transactions contemplated hereby;

          (b) The representations and warranties contained herein and in all
other Loan Documents, as amended hereby, shall be true and correct as of the
date hereof as if made again on and as of the date hereof (except if and to the
extent that such representations and warranties are or were expressly made only
as of another specific date);

          (c) All corporate proceedings taken in connection with this Amendment
and the other Amendment Documents, and all legal matters incident thereto, shall
be reasonably satisfactory to the Agent and its legal counsel, Jenkens &
Gilchrist, a Professional Corporation; and

          (d) No Default or Event of Default shall have occurred and be
continuing.

The Agent shall, promptly after all of the conditions precedent set forth in
this Paragraph 11 have been satisfied, so notify the Borrower and the Lenders in
writing. In the event that each of the aforesaid conditions precedent set forth
in this Paragraph 11 has not been satisfied on or before March 31, 1999, this
Amendment shall be of no force or effect.

     12. Representations and Warranties. Each of the Borrower and the other Loan
Parties hereby jointly and severally represent and warrant to, and agrees with,
the Agent and the Lenders that, as of the date of and after giving effect to
this Amendment, (a) the Subsidiaries of the Borrower identified on Schedule 1
hereto are the only Subsidiaries of the Borrower, and, with respect to each of
the Subsidiaries of the Borrower, the authorized Capital Stock, the par value
per share, the number of shares issued and outstanding and the owner(s) of such
issued and outstanding shares are as specified on such Schedule 1; (b) each
material action, suit, investigation or proceeding before or by any Governmental
Authority or arbitrator pending or, to the knowledge of any Loan Party,
threatened against or affecting any Loan Party or any Subsidiary of the Borrower
as of March 15, 1999, is disclosed on Schedule 2 hereto, and none of such
actions, suits, investigations or proceedings could, if adversely determined,
have a Material Adverse Effect or could adversely affect the ability of the
Borrower and the other Loan Parties to pay or perform their indebtedness,
liabilities or obligations under the Credit Agreement or the other Loan
Documents; (c) the execution, delivery and performance of this Amendment and any
and all other Amendment Documents executed and/or delivered in connection
herewith have been authorized by all requisite corporate action on the part of
the Borrower and the other Loan Parties and will not violate the Borrower's or
any Loan Party's corporate charter or bylaws; (d) the term Loan Documents as
defined in the Credit Agreement and as used in any of the Loan Documents
includes, without limitation, the Amendment Documents; (e) all representations
and warranties set forth in the Credit Agreement and in the Security Documents
are true and correct as if made again on and as of such date (except if and to
the extent that such representations and warranties were expressly made only as
of another specific date); (f) no Default or Event of Default has occurred and
is continuing; (g) Alpine Enterprises, Ltd. does not have assets valued at or
exceeding Cdn.$1,500,000 as of the Second Amendment Effective Date; and (h) the


<PAGE>   9


Credit Agreement, the Notes, the Guaranties, the Security Documents and the
other Loan Documents (as amended by this Amendment) are and remain legal, valid,
binding and enforceable obligations of the Borrower and the other Loan Parties
(as applicable) which are parties thereto in accordance with their terms.

     13. Governing Law. THIS AMENDMENT AND THE OTHER LOAN DOCUMENTS SHALL BE
GOVERNED BY, AND CONSTRUED IN ACCORDANCE WITH, THE LAWS OF THE STATE OF TEXAS
(WITHOUT REGARD TO CONFLICTS OF LAWS PRINCIPLES) AND APPLICABLE LAWS OF THE U.S.

     14. Counterparts. This Amendment may be executed in any number of
counterparts, all of which when taken together shall constitute one agreement,
and any of the parties hereto may execute this Amendment by signing any such
counterpart.

     15. No Oral Agreements. THIS AMENDMENT, TOGETHER WITH THE CREDIT AGREEMENT
AND THE OTHER LOAN DOCUMENTS AS WRITTEN, REPRESENT THE FINAL AGREEMENTS BETWEEN
AND AMONG THE PARTIES HERETO AND MAY NOT BE CONTRADICTED BY EVIDENCE OF PRIOR,
CONTEMPORANEOUS OR SUBSEQUENT ORAL AGREEMENTS OF THE PARTIES. THERE ARE NO
UNWRITTEN ORAL AGREEMENTS BETWEEN (A) THE BORROWER OR ANY OTHER LOAN PARTY AND
(B) THE AGENT OR ANY LENDER.

     16. Agreement Remains in Effect; No Waiver. Except as expressly provided
herein, all terms and provisions of the Credit Agreement and the other the Loan
Documents shall remain unchanged and in full force and effect and are hereby
ratified and confirmed. No waiver by the Agent or any Lender of any Default or
Event of Default shall be deemed to be a waiver of any other Default or Event of
Default. No delay or omission by the Agent or any Lender in exercising any
power, right or remedy shall impair such power, right or remedy or be construed
as a waiver thereof or an acquiescence therein, and no single or partial
exercise of any such power, right or remedy shall preclude other or further
exercise thereof or the exercise of any other power, right or remedy under the
Agreement, the Loan Documents or otherwise.

     17. Survival of Representations and Warranties. All representations and
warranties made in this Amendment or any other Loan Document shall survive the
execution and delivery of this Amendment and the other Loan Documents, and no
investigation by the Agent or any Lender or any closing shall affect the
representations and warranties or the right of the Agent and the Lenders to rely
upon such representations and warranties.

     18. Reference to Credit Agreement. This Amendment shall constitute a Loan
Document. Each of the Loan Documents, including the Credit Agreement, the
Amendment Documents and any and all other agreements, documents or instruments
now or hereafter executed and/or delivered pursuant to the terms hereof or
pursuant to the terms of the Credit Agreement as amended hereby, are (if and to
the extent necessary) hereby amended so that any reference in such Loan
Documents to the Credit Agreement shall mean a reference to the Credit Agreement
as amended hereby.


<PAGE>   10


     19. Severability. Any provision of this Amendment held by a court of
competent jurisdiction to be invalid or unenforceable shall not impair or
invalidate the remainder of this Amendment and the effect thereof shall be
confined to the provision so held to be invalid or unenforceable.

     20. Successors and Assigns. This Amendment is binding upon and shall inure
to the benefit of the Agent, the Lenders, the Borrower and the other Loan
Parties and their respective successors and assigns; provided, however, that
neither the Borrower nor any of the other Loan Parties may assign or transfer
any of its rights or obligations hereunder without the prior written consent of
the Lenders.

     21. Headings. The headings, captions and arrangements used in this
Amendment are for convenience only and shall not affect the interpretation of
this Amendment.

     22. Amendment Fee. The Borrower shall pay to the Agent, on or before the
date of this Amendment, an amendment fee in the amount of $325,000.00, which
amendment fee shall be divided pro rata amongst the Lenders based upon their
respective Commitments.


<PAGE>   11


     IN WITNESS WHEREOF, the parties hereto have caused this Amendment to be
executed and delivered by their duly authorized officers effective as of the day
and year first above written.

                                              THE BORROWER AND ITS SUBSIDIARIES:

                                              DYNAMEX INC.
                                              DYNAMEX OPERATIONS EAST, INC.
                                              DYNAMEX OPERATIONS WEST, INC.
                                              ROAD RUNNER TRANSPORTATION, INC.
                                              NEW YORK DOCUMENT
                                                EXCHANGE CORPORATION
                                              U.S.C. MANAGEMENT SYSTEMS, INC.
                                              DYNAMEX DEDICATED FLEET
                                                SERVICES, INC.
                                              and
                                              CANNONBALL, INC.


                                              By:
                                                     ---------------------------
                                              Name:  Jeffrey N. MacDowell
                                              Title: Vice President


                                              DYNAMEX CANADA INC.


                                              By:
                                                     ---------------------------
                                              Name:  Jeffrey N. MacDowell
                                              Title: Vice President


<PAGE>   12


                                              THE AGENT AND A LENDER:

Commitment:  $25,435,000                      NATIONSBANK, N.A.,
                                              individually and as the Agent

                                              By:
                                                     ---------------------------
                                              Name:  Frank Izzo
                                              Title: Senior Vice President


<PAGE>   13


                                              THE CO-AGENTS AND LENDERS:

Commitment:  $14,130,000                      BANKBOSTON, N.A.,
                                              individually and as a Co-Agent

                                              By:
                                                     ---------------------------
                                              Name:
                                                     ---------------------------
                                              Title:
                                                     ---------------------------


<PAGE>   14


Commitment:  $8,478,000                   BANK AUSTRIA CREDITANSTALT
                                          CORPORATE FINANCE, INC. FKA
                                          CREDITANSTALT CORPORATE FINANCE, INC.,
                                          individually and as a Co-Agent

                                          By:
                                                 -------------------------------
                                          Name:
                                                 -------------------------------
                                          Title:
                                                 -------------------------------


                                          By:
                                                 -------------------------------
                                          Name:
                                                 -------------------------------
                                          Title:
                                                 -------------------------------


<PAGE>   15


                                          ADDITIONAL LENDERS:


Commitment: $8,478,000                    THE BANK OF NOVA SCOTIA

                                          By:
                                                 -------------------------------
                                          Name:
                                                 -------------------------------
                                          Title:
                                                 -------------------------------


<PAGE>   16


Commitment: $8,478,000                    BANK ONE, TEXAS, N.A.

                                          By:
                                                 -------------------------------
                                          Name:
                                                 -------------------------------
                                          Title:
                                                 -------------------------------


<PAGE>   17


                                   SCHEDULE 1

                       SUBSIDIARIES OF THE BORROWER, ETC.


<TABLE>
<CAPTION>
                                                                                    Shares Issued and              Owner(s)
      Subsidiary                  Capital Stock             Shares Authorized          Outstanding                 of Shares
-----------------------    --------------------------     ----------------------   -------------------    -------------------------
<S>                        <C>                            <C>                      <C>                    <C>
Dynamex Canada Inc.                  Common;                Unlimited Common;          100 Common;        The Borrower owns 100% of
                                    Preferred              Unlimited Preferred     3,750,000 Preferred    the Common and Preferred
                                                                                                          Shares.

Dynamex Operations                   Common                   10,000 Common            1,000 Common       The Borrower owns 100% of
East, Inc.                                                                                                the Common Shares.

Dynamex Operations                   Common                   10,000 Common            1,000 Common       The Borrower owns 100% of
West, Inc.                                                                                                the Common Shares.

Road Runner                      Common (Voting;              25,000 Common        6,545 Voting Common;   The Borrower owns 100% of
Transportation, Inc.        Non-Voting; Undesignated)        (7,000 Voting;          4,363.9998 Non-      the Voting Common and
                                                            5,000 Non-Voting;         Voting Common       Non-Voting Common Shares.
                                                          13,000 Undesignated)

New York Document                    Common                    200 Common               150 Common        The Borrower owns 100% of
Exchange Corporation                                                                                      the Common Shares.

U.S.C. Management                    Common                  200,000 Common            91.33 Common       The Borrower owns 100% of
Systems, Inc.                                                                                             the Common Shares.

Alpine Enterprises, Ltd.      Class A Voting Common           Unlimited of             290 Class A        Dynamex Canada Inc. owns
                              Class B Voting Common            each class             Voting Common       100% of the Class A
                              Class C Voting Common                                                       Voting Common Shares.
                              Class D Voting Common
                            Class A Non-Voting Common
                            Class B Non-Voting Common
                            Class C Non-Voting Common
                            Class D Non-Voting Common
                                Preference Shares

Dynamex Dedicated Fleet              Common                      10,000                1,000 Common       The Borrower owns 100% of
Services, Inc.                                                                                            the Common Shares.

Cannonball, Inc.                     Common                      71,450                   69,350          The Borrower owns 100% of
                                                                                                          the Common Shares.
</TABLE>


<PAGE>   18


                                   SCHEDULE 2

                                LITIGATION, ETC.


1.   The information set forth on Schedule 7.6 to the Credit Agreement is
     incorporated herein by reference.

2.   In November and December 1998, two class action lawsuits were filed in the
     United States District Court for the Northern District of Texas, naming the
     Company and certain of its current and former executive officers as
     defendants. The lawsuits arise from the Company's November 2, 1998
     announcement that it was (i) revising its results of operations for the
     year ended July 31, 1998 from that which had been previously announced on
     September 16, 1998 and (ii) restating its results of operations for the
     third quarter of fiscal 1998 from that which had been previously reported.
     The complaints allege the defendants issued a series of materially false
     and misleading statements and omitted material facts concerning the
     Company's financial condition and business operations. The lawsuits allege
     violations of the Securities Act of 1933 and Securities Exchange Act of
     1934. The plaintiffs seek unspecified damages on behalf of all other
     purchasers of the Company's common stock during the period of December 3,
     1997 through and including October 30, 1998.

     On February 5, 1999, the Court entered an Order consolidating the actions
     and approved the selection of three law firms as co-lead counsel. Pursuant
     to an agreed upon schedule, a consolidated and amended complaint will be
     filed on March 22, 1999. At this date, no class has been certified nor has
     any discovery commenced. The Company is unable to determine the likely
     outcome of this matter or estimate the amount, or potential range of, loss
     with respect to this matter.