Question Unless otherwise posted, the maximum speed limit on a public highway is: Answers 20 mph. 30 mph. 45 mph. 55 mph. Explanation When driving on a public highway, the maximum speed limit is 55 miles per hour. If a different speed limit is posted, follow the posted speed limit. Pass your DMV Written Test with flying colors Take me to the cheat sheet New Mexico This questions appears in the following tests: New Mexico Practice Test 22 New Mexico Practice Test 18