New Mexico Statutes Chapter 66. Motor Vehicles § 66-7-304. County roads; authority to regulate speed limits

(1) the speed limit is deemed to be reasonable and safe under local conditions on the basis of an engineering survey and traffic investigation;

(2) the alteration of a speed limit is approved by the state transportation commission; and

(3) the county posts speed limit signs that conform to the specifications as set forth in the manual adopted by the state transportation commission before enforcing the speed limit.