<PAGE>
                                                                    EXHIBIT 10.8
                                RYDER TRS, INC.

                           1560 BROADWAY, SUITE 1800

                             DENVER, COLORADO 80202

March 17, 1998

To:    David Russell

From:  Ronald A. Rittenmeyer /s/ RONALD A. RITTENMEYER

RE:    AMENDMENT TO EMPLOYMENT AGREEMENT

In connection with the transactions contemplated by the Agreement and Plan of
Merger (the "Merger Agreement") dated as of March 4, 1998 by and among Ryder
TRS, Inc. (the "Company"), Questor Partners Fund, L.P., Questor Side-By-Side
Partners, L.P., Madison Dearborn Capital Partners, L.P., BDG Corporation and
Budget Group, Inc. (the "Merger"), the Company would like to recognize your
contribution to its success by amending your existing employment agreement dated
December 18, 1997 (the "Agreement"), as thereafter modified by letter dated
March 7, 1998 in which you waived all right and entitlement under the Agreement
to the "Executive Severance" and "Executive Stay-on Bonus" payments provided
therein.  In consideration of the foregoing, your Agreement is amended as
follows:

A.  MERGER BONUS:  Within 5 days following the "Closing Date" (as defined in the
      Merger Agreement), the Company will make a cash payment to you in the
      amount of $108,000.  On the later of October 1, 1998 or 120 days after the
      Closing Date, the Company will make an additional cash payment to you in
      the amount of $108,000.

b.  Executive Severance:  If during the 2-year period following the Closing Date
      (i) your employment is terminated by the Company for reasons other than
      the conviction of, or a plea of no contest to, a felony punishable by a
      prison sentence of more than one year, (ii) you terminate your employment
      by resigning following a reduction in base salary and/or a change to the
      existing Company's target maximum bonus percentage or formula, (iii) you
      terminate your employment by resigning following a requirement by the
      Company to relocate to a location more than 50 miles away from your
      current employment location, or (iv) you terminate your employment by
      resigning following a reduction in your title, duties, reporting
      relationships or responsibilities, the Company shall:

      *  Pay you a lump sum cash amount within 5 days of your date of
      termination equal to your then current annual base salary and prorated
      targeted maximum bonus for the year.
<PAGE>
 
      *  If your termination of employment is prior to May 1, 1999, pay you a
      lump sum cash payment within 5 days of your date of termination in the
      amount of $100,000.

      *  Make a lump sum cash payment to you within 5 days of your date of
      termination of any unpaid amounts required by Paragraph (a) above.

      *  Provide, without cost to you, health care coverage required by Sections
      601-608 of the Employee Retirement Income Security Act of 1974, as amended
      ("COBRA"), for a period of 12 months following your termination of
      employment. In lieu of COBRA coverage, you may elect to receive the
      applicable cost of such coverage in a lump sum cash payment, to be paid
      within 5 days of your termination of employment.

      *  If after May 1997 you relocated to the Denver, Colorado area at the
      Company's request, the Company will reimburse you for relocation expenses
      incurred following your termination of employment in an amount equal to
      the lesser of: (i) your actual expenses incurred in relocating from
      Denver, Colorado after your termination, or (ii) 125% of your expenses
      previously incurred in relocating to Denver, Colorado at the Company's
      request, provided any such expenses are not reimbursed by any subsequent
      employer. The foregoing relocation program will have the same benefits
      (including tax gross up on certain items) and coverage as the relocation
      program under which you were moved to Denver, Colorado by the Company.

C.  RETENTION BONUS:  If you are employed by the Company on May 1, 1999, the
      Company will pay you a lump sum cash payment in the amount of $100,000.

Anything herein to the contrary notwithstanding, the terms of this amendment to
your Agreement are subject to (i) the consummation of the transactions
contemplated by the Merger Agreement, and (ii) the approval of the holders of
record of at least 75% of the Company's outstanding voting common stock
immediately prior to the Merger in a manner that complies with Section
280G(b)(5)(B) of the Internal Revenue Code of 1986, as amended.  If the Merger
Agreement is terminated prior to the Closing Date as provided in Section 10.1 of
the Merger Agreement or the shareholder approval requirements described in the
preceding sentence are not satisfied, the terms of this amendment shall be void
and be of no further force and effect, and the existing terms of your Agreement
shall continue to apply without regard to this amendment.  Except as otherwise
provided herein, the terms of this amendment shall not affect any other benefits
provided under your Agreement.

                                      -2-
<PAGE>
 
All payments to be provided to you hereunder are subject to applicable federal
and state employment and income tax withholding obligations.

The terms of this amendment to your Agreement is tailored to you and therefore,
MUST BE TREATED AS STRICTLY CONFIDENTIAL.

If the terms of this amendment to your Agreement are acceptable, please
acknowledge your acceptance by signing each signature page to this amendment as
indicated below and returning one of the signed pages to me.

Agreed To And Accepted By:

/s/ DAVID RUSSELL     3/17/98
____________________________________
David Russell          DATE

                                      -3-