High voltage transmission is VERY costly underground.
Hawaii is not big. Its land is very expensive.
They priced bringing power from the western power plants ( fuzzed by Google Earth just north of the western end of H-1 freeway ) to urban Honolulu. ( The city and county of Honolulu covers the entire island.)
The price was a killer: 5 or more times as expensive as conventional overhead lines.
Even with this expensive real estate: it did not pencil out.
In high automobile traffic areas the advantage of underground service overwhelms its expense.
Thusly all highly urbanized areas go underground. It's to stop the nasty consequence of trucks and cars taking out a power pole.
And then when the real estate is fantastically expensive even the high voltage lines run underground.
Superconductors are being field tested -- even now -- for this duty. Thus all prior practice can be overturned. All superconducting schemes are intended for underground power transmission. ( It will require DC for superconditivity -- and inverters close by town.)
In our trade nothing is permanent.
