Piilani Highway is a must drive road in the world. Located in Maui, the second-largest of the Hawaiian Islands, USA, this highway is 38 miles long looping all the way around the southern coast of the island.
The road, known as Hawaii Route 31 is a twisty, up and down roller coaster of a ride. The toughest section of the road is about 20 miles long. The road is winding, in some places only wide enough for one vehicle, and in many places bordered by a drop of hundreds of meters over the sea, unprotected by guardrails. In some areas (such as at Lelekea Bay) it's just a one-and-a-half lane bumpy road hugging the sea cliff around a blind curve. Fences have been installed on the mountain here to prevent rocks from falling onto cars. The mountain side is literally held by chains on the right at places, to avoid falling rocks from hitting the motorists. The hairpin bends are completely blind, but there is almost no traffic. Occasionally the dirt road past Route 31 is closed to traffic due to landslides. Most major rental car contracts forbid driving this section. However, although it is somewhat rough in places, it is by no means a daunting or particularly dangerous road if taken slowly.
The road's winding design, providing stunning panoramic views, is very curvy and fun for a leisurely ride, so it pays to take it slow. It’s not a gravel road, instead, it looks more like a very old paved road that’s been patched over and over and over again with asphalt. After rain, even a single rainfall, conditions of the road can be challenging. Adverse weather conditions can prompt closure of the road. Some parts are washboard-like and require speeds of 5 mph (8 km/h) or less in order to avoid damaging the suspension of a rental car. This prohibition in rental car contracts seems more related to the remoteness of this section of highway; in case of a breakdown, there is very little in the way of passing traffic or inhabitants around, and no cell phone service in parts.