Question Unless otherwise posted, the maximum speed limit on a rural interstate highway is: Answers 40 mph. 55 mph. 75 mph. 85 mph. Explanation When driving on a rural interstate highway, the maximum speed limit is 75 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 16 New Mexico Practice Test 22