It’s been an extremely rough ride on the Honolulu Authority for Rapid Transportation train these days.

That means everything from the current federal investigation into project spending, and high-profile reports of safety concerns: a whistleblower’s account of construction quality control, and potentially invalid rail-car roof and fire testing.

These have produced furrowed brows, so there’s broad public empathy for the impulse to get off at the earliest stop possible. That, based on recent discussions, would be the Middle Street station, a crucial 5 miles short of the elevated rail project’s planned terminus at Ala Moana Center.

Now is the time to stop, of course — stop and think about what that would entail. The bottom line is that stopping construction that far short of the planned project scope is a nonstarter, costing more than it saves.

The latest discussion on this front originated in City Council chambers, with Councilwoman Heidi Tsuneyoshi sending a query on comparative costs to HART. Her specific request was that HART provide an estimate of the cost if the project were to stop at Middle Street but would include construction of the Pearl Highlands Parking Garage.

The answer, according to HART Executive Director and CEO Andrew Robbins, is that costs of the shortened route would be an estimated $8.579 billion. Simple math tells the public that this is about $450 million less than the currently projected total of $9 billion to reach Ala Moana.

But things aren’t that simple.

The system Honolulu would get would not be what the city proposed to the Federal Transit Administration to get its subsidy of $1.55 billion. Robbins’ rational assumption is that the FTA would demand the city refund that subsidy.

Further, changes could require additional studies beyond what’s in the environmental impact statement — studies that will add to the cost and delay.

The ridership would have to be re-evaluated, for starters. Would the foreshortened rail project attract the same number of riders who would have to get off the train and complete their trip via ground transportation, bogged down in traffic? Definitely not.

Finally, HART anticipates there could be legal claims against it for the major changes. That risk must be acknowledged, even if it’s harder to quantify. Although actual construction of the town-side guideway has not yet begun, HART spokesman Bill Brennan said there is already a $400 million contract, won by Nan Inc., to relocate utilities in the City Center segment of the rail.

However, it also must be acknowledged that recent events have left the taxpaying public feeling anything but reassured about the project.

Take the fire testing. HART’s contractor, Hitachi Rail Italy, has questioned the validity of the tests that showed the cars not withstanding heat. The heat was controlled manually and was increased much more quickly than called for; a retest under automated laboratory conditions is planned.

Still, that leaves one wondering why such an error in testing protocols was made. Full transparency in the conduct of the repeat tests will be essential.

On the well-publicized federal grand-jury subpoenas for construction records, HART points to exchanges it has had with potential bidders for the City Center segment, in which no questions on the probe were asked. Of course, it still could remain a concern, suppressing interest from risk-averse bidders.

HART must remain aware of these fault lines, and address them fully in pursuing the only acceptable outcome: a rail system that gets people where they want to go. For the vast majority, that is not Middle Street.