<PAGE>   1
                                                                    Exhibit 10.1


                       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 


<PAGE>   9


(h) the 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:   Tony Zhang
                                        Title:  Vice President



<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:  Robert M. Biringer
                                             ----------------------------------
                                        Title: Executive Vice President
                                              ---------------------------------


                                        By:
                                           ------------------------------------
                                        Name:  John G. Taylor
                                             ----------------------------------
                                        Title: Senior Associate
                                              ---------------------------------


<PAGE>   15



                                        ADDITIONAL LENDERS:

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


                                        By:
                                           -------------------------------------
                                        Name:   F.C.H. Ashby
                                             -----------------------------------
                                        Title:  Senior Manager - Loan Operations
                                              ----------------------------------



<PAGE>   16



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

                                        By:
                                           ------------------------------------
                                        Name:   Mark B. Wade
                                             ----------------------------------
                                        Title:  Vice President
                                              ---------------------------------


<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.