When local transit officials started planning Oahu’s elevated rail project, they envisioned a flexible system that could run trains of two, three and four cars from the instant the rail line started operating — a way to adjust to growing ridership and periods of greater demand.

However, after awarding a $1.4 billion contract in 2011 to Ansaldo Honolulu JV to design, build, operate and maintain that system, the local agency overseeing the rail project realized that’s not what Oahu would get.

Instead, Ansaldo designed a rail system that would run only two-car trains. The city could eventually add more cars to those trains — but to do so the system would face weeks of extensive "service interruptions," according to documents obtained by the Honolulu Star-Advertiser.

Those documents, provided by a Honolulu Authority for Rapid Transportation consultant, show that HART and Ansaldo have locked horns over train configurations since at least August 2012.

HART officials say the two-car train system that Ansaldo designed was unacceptable. Under what the firm had proposed, "you might have to shut the line down for some time" to convert those trains to greater lengths, HART Deputy Director for Systems Rainer Hombach said Friday, although he said he didn’t have an estimate on how much time.

For more than a year now, HART has quarreled with Ansaldo Honolulu, a joint venture of Italian-based firms AnsaldoBreda and AnsaldoSTS that beat out two other competitors vying for the massive scope of work, over whether the firm is complying with its contract.

Now, HART is moving ahead with a change to avoid any service shut-downs to convert the trains — and a plan that it thought would swiftly move the project past the dispute with Ansaldo.

It recently instructed the firm to build 20 four-car trains instead of the 40 two-car trains. Both approaches would use the same total number of rail cars (80). When they’re built, Oahu’s rail stations will be able to handle trains of up to four cars.

On Friday, Dan Grabauskas, HART’s executive director, said the city should have just asked for the four-car train design from the start. Grabauskas, who joined HART in 2012, said he doesn’t know why previous local rail leadership opted for two- and three-car trains as well.

But the change to four-car trains hasn’t resolved the dispute, and HART and Ansaldo remain miles apart on the cost of those changes.

HART estimates switching to four-car trains will save the city some $20 million, which it wants Ansaldo to apply as credit in its contract for not creating a more flexible rail system.

Ansaldo disputes it owes a credit, and in a Sept. 27 report it estimated the change to four-car trains would actually cost the city more money — $4.2 million, due to added design, production and labor and other costs.

"We are just following the usual contract change process," Enrico Fontana, project manager for Ansaldo Honolulu JV, said in an email Friday. "Our top priority is to have engineers and vendors moving forward full steam, in order to deliver the first train as soon as the maintenance and storage facility (in) Waipahu is ready."

The firm will start building the trains in a few months, Fontana added. He did not respond to questions about the contract dispute, or the original two-car system Ansaldo had proposed.

With the two sides about $25 million apart, Grabauskas acknowledged that’s a big gap, but he added HART regularly finds itself negotiating down contractors’ price estimates on the project.

Grabauskas said he was confident the city would not pay Ansaldo any additional money to make the change.

"The contract was very clear. The city was adamant, and you bid that you were going to do two- and three- and four-" car trains, he said Friday. "That should be a credit to us. We’ve spent more than six months looking at this."

The move to four-car trains was also recently approved by federal transit officials under a federal $1.55 billion agreement to help Oahu’s $5.26 billion rail project. The rest is covered by an Oahu general excise tax surcharge.

HART officials will update the board of directors on the four-car change on Thursday. Their presentation will include the $20 million HART expects to save — but not Ansaldo’s approximately $4 million cost estimate, Grabauskas said.

ADDITIONALLY, QUESTIONS remain over how many riders Oahu’s rail system would gain in its first decade of use with four-car trains compared to two-car trains.

HART has said the wait time for passengers would increase from 2.8 minutes with a two-car train to 5.6 minutes with a four-car train, but has also touted multiple advantages with going to four-car trains: The plan, Grabauskas says, will make more seats available and allow the system to work better for disabled passengers.

A Sept. 27 white paper supporting the plan estimates a net annual savings of up to $285,000 in operational costs — even after nearly $1 million in added energy and maintenance costs for running more cars and added wear-and-tear.

While several documents and correspondences by HART and their consultants have cited gains in ridership by switching to four-car trains, a HART project consultant who’s helped oversee the trains’ engineering during the past year called those ridership gains misleading.

The four-car trains would actually see 11 percent fewer new riders than if the system ran the two-car trains, said Mike Bogonovich, a systems engineer with HDR/InfraConsult.

Recently conducted ridership models from outgoing rail consultant Parsons Brinckerhoff show that 104,300 daily riders would use rail with a four-car train design in its opening year — compared to 117,000 daily riders on a two-car train design, according to several of Bogonovich’s email exchanges with Parsons Brinckerhoff employees.

In 2030, the system would have 119,600 daily riders on four-car trains and 133,800 in two-car trains, those emails show.

"They should have reported that" when touting the four-car plan, Bogonovich said Friday. He further called HART’s estimated operational savings "smoke and mirrors" unless Ansaldo agrees with them.

Bogonovich said he will be leaving the project at the end of the year to work for Los Angeles-based firm LTK Engineering Services. His departure from the Oahu rail project, Bogonovich added, was expected as his phase of the project came to an end.

Liz Scanlon, HART’s director of planning, utilities and right of way, said she hasn’t seen any such updated ridership numbers for the two-car trains. However, "it’s fair to assume" there’d be more ridership gains with the two-car train design than the four-car model, Scanlon said Friday.

Grabauskas said it wasn’t necessary to provide such an analysis to federal transit officials when seeking their approval for the plan. Even if a four-car train design won’t net as many riders, the plan still makes sense overall, he said.

"What we needed to show was … the package of positives outweighed the decision," Grabauskas said Friday. "When we look at this, this was the right decision. There’s no way this decision doesn’t save us money."