Exhibit 5.1

                                  April 6, 2004

Board of Directors
Swift Transportation Co., Inc.
2200 South 75th Avenue
Phoenix, Arizona 85043

Ladies and Gentlemen:

         We have acted as counsel to Swift Transportation Co., Inc., a Nevada
corporation (the "Company"), in connection with the preparation and filing with
the Securities and Exchange Commission of the Company's Registration Statement
on Form S-3 (the "Registration Statement") under the Securities Act of 1933, as
amended, relating to the sale, from time to time, by certain stockholders of the
Company (the "Selling Stockholders") identified in the prospectus (the
"Prospectus") which forms a part of the Registration Statement, in the manner
described in the Prospectus, of up to an aggregate of 942,155 shares of the
Company's common stock, par value $.001 per share (the "Shares").

         In so acting, we have examined originals or copies (certified or
otherwise identified to our satisfaction) of the Registration Statement, the
Prospectus and such corporate records, agreements, documents and other
instruments, and such certificates or comparable documents of public officials
and of officers and representatives of the Company, and have made such inquiries
of such officers and representatives, as we have deemed relevant and necessary
as a basis for the opinions hereinafter set forth.

         In such examination, we have assumed the genuineness of all signatures,
the legal capacity of all natural persons, the authenticity of all documents
submitted to us as originals, the conformity to original documents of all
documents submitted to us as certified, conformed or photostatic copies and the
authenticity of the originals of such latter documents. As to all questions of
fact material to these opinions that have not been independently established, we
have relied upon certificates or comparable documents of officers and
representatives of the Company.

         Based on the foregoing, and subject to the qualifications stated
herein, we are of the opinion that the 942,155 Shares covered by the Prospectus
have been duly authorized and validly issued, and are fully paid and
non-assessable.

         The opinions expressed herein are limited to the corporate laws of the
State of Nevada and we express no opinion as to the effect on the matters
covered by this letter of the laws of any other jurisdiction.



Board of Directors
Swift Transportation Co., Inc.
April 6, 2004
Page 2

         We hereby consent to the use of this letter as an exhibit to the
Registration Statement and to any and all references to our firm in the
Prospectus which is a part of the Registration Statement.

         We also consent to the incorporation by reference of this opinion in
any related registration statement filed by the Company pursuant to Rule 462(b)
of the Securities Act.

                                    Very truly yours,

                                    SNELL & WILMER, L.L.P.