The Federal Transit Administration says it will demand its money back if rail does not reach Ala Moana Center.

Both mayoral candidates now say the city has no choice but to do what the Federal Transit Administration says.

Fortunately, neither the FTA nor the winner of the mayoral election will decide rail’s fate. Legislators and City Councilmembers will decide whether to raise taxes enough to cover the cost.

These decision-makers should address four questions:

>> How much more money is needed to finish rail?

>> Where will that money come from?

>> What will be accomplished?

>> What could be accomplished if the same amount of money is spent on something else?

We believe that they will reach the following conclusions:

>> Another $5.75 billion, over and above the non-recoverable $3.5 billion already spent, will be needed to reach Ala Moana Center (i.e., total construction costs of $10.8 billion, less $3.5 billion already spent or irretrievably committed, less $1.55 billion federal money yields $5.75 billion).

>> The chances of getting an additional federal grant are virtually nil.

>> The private sector will not provide more than an insignificant portion of the needed money.

>> The bulk of the new money will have to comefrom local residents, who will pay an average of $200 per person ($800 for each family of four) every year until construction ends.

>> The rest — roughly 15 percent of $5.75 billion — will come from tourists or other nonresidents.

>> After construction ends, each family of four will continue to pay an average of $800 per year, to operate and maintain the rail system.

>> Traffic congestion will be much worse when rail becomes fully operational than it is now.

Those who question this last statement should see the final environmental impact study in where the city admits, “traffic congestion will be worse in the future with rail than what it is today without rail.”

Other ways to spend the money: Working together, the city and state could reduce traffic congestion, for example, by aggressively adding new traffic lanes to existing roads, as has already been done on the central part of H-1 Freeway; by installing flyovers and bypasses in chokepoint areas like the Middle Street merge; and by adding new contra-flow and bus-on-shoulder options. Each is a proven strategy that, unlike rail, would benefit all commuters.

The city could also afford to greatly improve its award-winning bus system. This might include increasing the number of express buses that go where commuters want to go, rather than eliminating most of them as is part of the rail plan.

All of the above could be done for less than half of the money saved by pulling the plug on rail now. The Legislature and City Council could spend the rest on other areas of need, such as a comprehensive homeless plan, improvements for our schools, sewer and road repairs — or simply leave it in the pockets of island residents.

The existing guideway could be modified for walking, biking and other community activities, and provide unique views. New York City’s High Line is a wildly popular public park built on an abandoned rail line. While no one would set out to spend $3.5 billion for a High Line trail/park in Hawaii, it could become a tourist attraction.

Twenty years from now, traditional mass transit will be functionally obsolete for cities like Honolulu thanks to autonomous vehicles and ride-hailing apps.

Who’s the future of urban transportation: Apple, Google and Uber, or Kirk Caldwell, the FTA and the Honolulu Authority for Rapid Transportation?

Panos Prevedouros is a civil engineering professor at the University of Hawaii at Manoa. Randall Roth is a law professor at UH-Manoa.