UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-K ☒ ANNUAL 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 fiscal year ended December 31, 2022 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 Str ...