Overview of Waipiʻo Valley on the island of Hawai‘i, in Hawaii. The valley floor at sea level is almost 2,000 ft (610 m) below the surrounding terrain. A steep road leads down into the valley from this lookout point and loses 800 vertical feet (244 m) in 0.6 miles (0.9 km) at a 25% average grade, with steeper grades in sections. This is a public road but it is only open to 4WD vehicles. It is the steepest road of its length in the United States.