Question Unless otherwise posted, the speed limit on the interstate is: Answers 55 mph. 70 mph. 80 mph. Explanation When driving on the interstate, the statutory speed limit is 70 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 Alabama This questions appears in the following tests: Alabama Practice Test 20 Alabama Practice Test 8