Trick question. Top speed limit is 75 miles per hour. =D
Only in lesser states...
http://www.mysanantonio.com/news/local/article/Texas-ranks-fastest-in-nation-5705723.php
They just raised the speed limit on rural interstate sections to 80 MPH here in Idaho. I did hear that the state police are enforcing it pretty strictly, too - the "5 MPH rule" doesn't apply any more.