1
                                                                       Exhibit 5

                           [SNELL & WILMER LETTERHEAD]

                                  May 15, 2001

Swift Transportation Co., Inc.
220 South 75th Avenue
Phoenix, Arizona 85043

Ladies and Gentlemen:

      You have requested our opinion with respect to certain matters in
connection with the filing by Swift Transportation Co., Inc. (the "Company") of
a Registration Statement on Form S-3 on May 15, 2001 with the Securities and
Exchange Commission, covering the offering of up to 1,320,000 shares of the
Company's common stock, $.001 par value (the "Shares").

      In connection with this opinion, we have examined the Registration
Statement and related Prospectus, your Articles of Incorporation and Bylaws, as
amended, and such other documents, records, certificates, memoranda and other
instruments as we deem necessary as a basis for this opinion. We have assumed
the genuineness and authenticity of all documents submitted to us as originals,
the conformity of originals of all documents submitted to us as copies thereof,
and the due execution and delivery of all documents where due execution and
delivery are a prerequisite to the effectiveness thereof.

      On the basis of the foregoing, and in reliance thereon, we are of the
opinion that the Shares, when issued and sold as described in the Registration
Statement, will be validly issued, fully paid, and nonassessable.

      We hereby consent to the filing of this opinion as an exhibit to the
above-referenced Registration Statement and to the use of our name wherever it
appears in the Registration Statement, including the Prospectus constituting a
part thereof. In giving such consent, we do not consider that we are "experts"
within the meaning of such term as used in the Securities Act of 1933, as
amended, or the rules and regulations of the Securities and Exchange Commission
issued thereunder, with respect to any part of the Registration Statement,
including this opinion as an exhibit or otherwise.

                                    Very truly yours,

                                    Snell & Wilmer, L.L.P.

                                    /s/ Snell & Wilmer, L.L.P.

 Member: LEX MUNDI, a global association of independent law firms with members
          in the United States and 60 countries throughout the world.