Rail board members are now openly questioning whether narrow Dil­lingham Boulevard would be the best path on which to build the island’s transit system heading into town, as the project faces huge costs and the community braces for the impacts of building through that crowded corridor.

“Whoever planned this had to have known they would have problems with this,” Honolulu Authority for Rapid Transportation Board Chairwoman Colleen Hanabusa said during a special public meeting Tuesday to discuss the costly overhead utility line clearance problems that are helping to significantly drive up costs for the project.

Hanabusa suggested Nimitz Highway as an alternative. Rail officials previously selected Dillingham Boulevard in part because the state Department of Transportation was planning to extend the airport viaduct farther Diamond Head along Nimitz Highway, HART Deputy Director Brennon Morioka told Hanabusa and other members of the board’s Project Oversight committee.

Morioka served as the DOT director when the state agency was looking at extending the viaduct along Nimitz Highway. Asked by Hanabusa whether he would have picked the busy Dil­lingham Boulevard corridor to run rail’s elevated guideway, Morioka said that he didn’t want to “second-­guess” the decision by his predecessors at HART. After the meeting he said that board members have instructed him to look into the idea of running rail along Nimitz Highway — and whether it’s a viable alternative — before the board’s next special meeting, to be held June 8.

At that meeting board members plan to discuss the future of the project, and what its final size and scope might be now that it’s running vastly over budget again.

Federal officials now estimate the price could be $8.1 billion to complete the full 20-mile project. At Tuesday’s evening meeting, city rail officials explained the budget situation could be even more dire: Rail’s federal partners actually estimate there’s a 65 percent chance that the project will be completed within that price, according to Mike Formby, the city’s Department of Transportation Services director and chairman of the HART board’s Project Oversight Committee.

That would indicate there’s a 35 percent chance the project could cost even more than $8.1 billion under the Federal Transit Administration estimate. Details on that price estimate are expected to be released next month, after HART and the FTA sort out their differences on their respective estimates.

The notion of changing the Dillingham Boulevard plan raises questions on what would happen with all the strips of property that HART has spent about $13 million or so to purchase along the boulevard. The Blood Bank of Hawaii, for example, has already started moving out of its Dillingham Boulevard facility and remains locked in a disagreement with HART officials over whether the rail agency should take the whole property.

HART officials have estimated it would cost at least $120 million to run utility lines underground along Dil­lingham Boulevard so that Hawaiian Electric Co. workers have the clearances they need to maintain the utilities — although rail officials say those numbers are sure to climb.

At the meeting, Formby said that the board wanted to see construction budgets that reflected the “worst-case scenario,” where no matter what happens once the construction starts, “we’re protected.”

Morioka agreed. He later said that HART is using a worst-case scenario of an additional $200 million to route overhead HECO lines underground from East Ka­polei to Aloha Stadium if the bucket trucks and other maintenance equipment they’re testing fail to meet HECO’s safety standards.

“I take it that’s different than what we’ve done in the past,” Formby said of HART’s using worst-case budget figures.

“To some degree,” Morioka replied.

Construction workers could face more challenges with the utility lines under Dillingham Boulevard as well as overhead, officials said. Crews have already dug 22 so-called “potholes” along the last five miles of the rail line through town to verify that utilities are located as drawn in the plans. Only three of those holes showed utilities in their proper places, Morioka said.

HART has further reached an agreement with HECO where rail work can overlap by a year with the effort to route the utility company’s overhead lines underground, Morioka said. Even with that deal in place, rail construction is certain to fall even further behind schedule in part due to the deeper shafts that must be drilled heading into town, he added. The FTA has estimated the project won’t be completed until 2024. Only a few years ago, HART had estimated it would finish in 2019.