Question to Google: How do you double a number?

Google answer: "Multiple by 2 or add it to itself."

Real-life example: If Honolulu’s planned heavy rail transit line was estimated to cost $3 billion, how much would it cost if the number was doubled?

Answer: $6 billion.

That is the current real world Honolulu’s rail line operates in, but it could change. It could more than double as construction edges toward town.

In a letter to the editor on Aug. 19, 2006, in The Honolulu Advertiser, then-Mayor Mufi Hannemann promised a "minimal operable system."

"The transit system the city ultimately will support will meet our immediate needs and our budget, estimated at around $3 billion."

"I want to be careful that we do not exceed our financial limits," the former mayor said.

By 2010, outgoing Gov. Linda Lingle was saying the system, which had shot up in estimated cost to $5.3 billion was just too expensive.

"To knowingly go into a project that is going to burden people financially for a generation to come, again, a project that the community perhaps cannot afford, I think there needs to be adjustment," Lingle said.

Three years ago, when Kirk Caldwell won against former Gov. Ben Cayetano to become mayor of Honolulu, rail’s future was the issue. Cayetano warned that rail was likely to wind up costing $7 billion.

Caldwell had all of Honolulu’s business and development interests backing him, and the labor unions and others were moving to support him, mostly because of his support of rail. At the time, the rail caveat tossed out by the Manoa Democrat was a vague pledge to "build rail better." It was never disclosed if he meant a nicer grade of concrete or a less expensive plan or a more thoughtful route.

In a December 2012 FedWatch interview, Caldwell said his plan focused on making the transit system more open and transparent.

"There’s been a lot of pushback. I think a lot of it had to do with the fact that the city became disengaged with the community on rail," Caldwell said. As for the rising costs, the then-mayor-elect brushed it off, prescribing "greater fiscal control and really watching everything that goes out — the change orders, the delays."

Caldwell seemed focused on somehow hiding the concrete, view-erasing leviathan of a mass transit system.

"Can we make it blend with the color of the buildings? Can we plant trees along it so they hide the elevated portion? Can the elevated parts be brought down so it interacts with the street level? Can sound barriers be tempered glass instead of concrete?" Caldwell said in the 2012 interview.

By 2014, the only elevated worry was the rising costs.

Last year, the Honolulu Authority for Rapid Transportation board was greeted with a new report warning that the $5.26 billion rail project could wind up costing taxpayers 10 to 15 percent more than budgeted.

"We’re going to be exploring every single option, with no promises, but we’re going to look," Caldwell said in response to the news.

Now comes the latest HART report tacking an estimated $200 million onto the already-$910 million shortfall, making the project a full $1 billion more than promised.

While the cost was pushed up, the finished date was pushed back — by another year. The end date is now 2021. When first sold to voters and the Legislature, the first section was supposed to open in 2017, an estimate long since cancelled.

According to the letter from HART officials to the city, the new effort is the somewhat mystifying question of: "How to best value engineer the remaining project in terms of maximizing cost efficiencies while maintaining a quality project."

It is obvious the rail project can’t be stopped, but the question remains, Can we pay for it?

Richard Borreca writes on politics on Sundays, Tuesdays and Fridays. Reach him at rborreca@staradvertiser.com.