 This revised interstate alignment traverses through an entirely rural area with extremely rugged terrain.Opened in 1988, this final portion is long and cost approximately $300 million to construct, making it one of the most expensive segments of Interstate Highway in the United States at $7.8 million per mile.It has some extremely rugged terrain, with one segment boasting a 7% grade downhill eastbound for seven miles (11 km) at Sandstone Mountain.