The Slater/Roth argument re self-driving cars falls apart immediately when you consider where those marvelous autos would drive -- in the same congested streets and highways Oahu has now. Maybe it's time to reassess the proposal once made by E. Alvey Wright, Hawaii's Director of Transportation in the 1970s (you could look it up). He said there should be a limit on the number of vehicles each household can own.. Predictably, that was shot down immediately. But without a grade-separated commuting option, Honolulu remains with too many traffic-related problems and too few solutions   
What can be done right now to finish this project is to gather financial commitments from landowners and corporations that will benefit enormously from rail. It's almost a case of malfeasance for the City to not have factored In this funding source by now. Frank Fasi, for all his quirkiness, sought such public/private plans from the five companies that bid on his elevated rail project in the early 1990s.