Mauna Kea Access Road (Hidden Hawaii Route 210)

Mauna Kea Access Road is a 14.96 highway corridor located on the Hawaiian Big Island. The highway begins at Hawaii Route 200 (the Saddle Road) and ascends to 13,780 feet above sea level near the summit of Mauna Kea. The original 6 miles of Mauna Kea Access Road was constructed during the early 1950s and expanded to the summit observatory facilities by 1976. As of 2022 the first 6 miles of Mauna Kea Access Road have been designated as the Hawaii Route 210 (which is not field signed). The remaining portion of the highway north of the Visitor Information Station is accessible to four-wheel drive vehicles and alternates between gravel/asphalt surfaces.

Part 1; the history of Mauna Kea Access Road

Mauna Kea is a dormant shield volcano located on the Hawaiian Big Island. The peak of the volcano reaches 13,803 feet above sea level. If measured from the ocean floor the prominence of Mauna Kea is 30,610 feet which surpasses that of Mount Everest.

Mauna Kea is thought to have begun to form under the Hawaiian volcanic hotspot approximately 1,000,000 years ago. The volcano entered its shield stage approximately 500,000 years ago which is when it became extremely active. The post-shield phase of the volcano began 200,000-250,000 years ago and it is last thought to have erupted 4,500-6,000 years ago.

Traditionally Mauna Kea was only accessible by overland trail. The first recorded ascent of Mauna Kea was in 1823 by Joseph Goodrich. It is thought that the summit had been regularly ascended by Native Hawaiians prior to European contact. By 1873 a dirt roadway had been constructed from Waimea to Humuula Sheep Station at the southern foot Mauna Kea near the summit trail. This early road was connected to a foot trail east to Hilo.

The Mauna Kea Trail can be seen prominently on the 1930 Hilo Chamber of Commerce map of the Big Island.

Mauna Kea became much more accessible following the U.S. Army's construction of the Saddle Road (Hawaii Route 200) which was constructed in 1943 and made a public highway in 1945. Part of the lower Mauna Kea Trail would be incorporated into the initial portion of what is now Mauna Kea Access Road. This early roadway would be used to reach the University of Hawaii's Mauna Kea Observatory which was founded in 1964.

The early Mauna Kea Access Road can be seen north of the Saddle Road (then Hawaii Route 20) on the 1959 Gousha Highway of Hawaii.

Mauna Kea Access Road can be seen terminating at Hale Pohaku Ranger Station (approximately 9,300 feet above sea level on the 1956 United States Geological Survey map of Mauna Kea. The Hale Pohaku Ranger Station in modern times have been expanded into the Mauna Kea Visitor Information Station.

Mauna Kea Access Road was extended north of Hale Pohaku Ranger Station in 1976 to 13,780 feet above sea level near the summit according to Oscar Voss's hawaiihighways.com. The roadway was constructed at the behest of the University of Hawaii by the Hawaii Department of Transportation. The road grade north of Hale Pohaku Ranger Station was initially completely dirt and was fully maintained by the University of Hawaii.

The completed Mauna Kea Access Road can be seen terminating the Mauna Kea Observatories on the 1982 United States Geological Survey map of Mauna Kea.

Mauna Kea Access Road appears as Hawaii County Route 210 on the 2012 Hawaii Department of Transportation Federal Aid System. The corridor is noted to be a 14.96-mile Minor Collector with a proposed Federal Aid classification change to Local. The Hawaii Department of Transportation seemingly disputed the classification change as the corridor was listed as the only access to the Mauna Kea Observatories.

The first 6 miles of Mauna Kea Access Road from Hawaii Route 200 to Mauna Kea Visitor Information Station appears as Hawaii Route 210 on the 2022 Hawaii Department of Transportation inventory log for the Big Island.

Mauna Kea Access Road north of the Visitor Station is mostly paved save for some gravel segments. Conjecture has it that the gravel portion is kept as a deterrent to tourists attempting to summit Mauna Kea. The roadway is open to traffic equipped with four-wheel drive vehicles. The four-wheel drive requirement seemingly has been justified due to 15% gradients claimed to be on the road above the Visitor Station. As of 2024 Enterprise Rental Car branded companies prohibit access to Mauna Kea Observatory Road north of the Visitor Station in their vehicles.

Part 2; a drive on Mauna Access Kea Access Road

Below the junction of the Saddle Road (Hawaii Route 200) and the Hawaii Route 210 portion of the Mauna Kea Access Road can be seen.

As northbound Mauna Kea Access Road traffic begins is warned of the prohibition to non-four-wheel drive vehicles 6 miles ahead. The Hawaii Route 210 portion of the corridor is currently not signed by the Hawaii Department of Transportation.

Traffic at the north end of the Hawaii Route 210 maintained portion of Mauna Kea Access Road is warned of the four-wheel drive requirement (Josh Schmid photo). Shuttles are arrival to the summit from the Mauna Kea Visitor Information Station.