UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 Form 10-Q ☒ Quarterly Report Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 or ☐ Transition Report Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 For the Quarter ended March 31, 2023 Commission File Number 0-15010 MARTEN TRANSPORT, LTD. (Exact name of registrant as specified in its charter) Delaware 39-1140809 (State of incorporation) (I.R.S. employer identification no.) 129 Marten Street ...