Part 1; the history of Hawaii Route 36A
As noted in the intro part of Hawaii Route 36A exists on a disconnected segment of Haleakala Highway from Hawaii Route 36/Hana Highway to Keolani Place/Dairy Road. The Hawaii Territory maintained portion of Haleakala Highway was completed to the boundary of Hawaii National Park (now Haleakala National Park) began to be constructed by 1929. Haleakala Highway would be completed to the 10,023-foot summit of Red Hill atop Haleakala when the National Park Service opened their segment during 1935.
Following the attack on Pearl Harbor on Oahu on December 7, 1941, the military presence in Hawaii Territory was immediately bolstered. Although the main influx of military activity in Hawaii Territory was centered around Oahu there also was a military presence on Maui. During 1942 construction of Naval Air Station Kahului began and established many roads around the facility. It is likely that what is now Keolani Place was constructed as part of Naval Air Station Kahului.
Following the conclusion of World War II, Naval Air Station Kahului was turned over to the Hawaii Aeronautics Commission. The facility was converted to civilian usage and reopened during June 1952 as Kahului Airport. Haleakala Highway east from Hana Highway to Dairy Drive and Keolani Place can be seen on the 1954 United States Geological Survey connecting as the primary access roadway to Kahului Airport.
The Island of Maui seemingly was not part of the original World War II era Hawaii Route System. Circa 1955 the United States Bureau of Public Roads renumbered the Hawaii Route System. The 1955 Hawaii Route Renumbering saw most of the conventions utilized by the current Hawaii State Route System established. Primary Hawaii Routes were given two-digit numbers whereas Secondary Hawaii Routes were given three-digit numbers. The Hawaii Routes were assigned in sequence for what Island/County they were located on coupled with what Federal Aid Program number they were tied to. In the case of the Island of Maui it was assigned numbers in the range of 30-40.
Kahului Airport can be seen on the 1959 Gousha Map of Hawaii without a Hawaii Route directly serving it.
According to hawaiihighways.com Keolani Place was added to the State Highway System during the 1960s as Hawaii Route 396 as it was the primary access road to Kahului Airport. Haleakala Highway east from Hana Highway through Kahului Airport may have been signed as Hawaii Route 37 and Military Route 37.