The ongoing legal fight over rail in U.S. District Court now boils down to one key issue — and it could make or break the project.

Did rail officials follow proper procedure in selecting the route to Ala Moana Center instead of a route to the University of Hawaii-Manoa campus as originally envisioned?

Judge A. Wallace Tashima listened to impassioned arguments on the matter Thursday during a hearing tied to part of a lawsuit by anti-rail coalition Honolulutraffic.com to stop the $5.26 billion elevated rail project.

That group contends that the city’s chosen route, which runs along Nimitz Highway in front of Chinatown, will mar the historic district by blocking harbor views. Opponents further assert that the project’s latest studies dismissing the alternative route to UH-Manoa, which would avoid Chinatown by tunneling underground, are "arbitrary" and "capricious."

Attorneys for the rail project countered in court that the rail studies of the alternative route, first ordered by Tashima in 2012, were a "fair, objective, reasoned analysis."

What Tashima ultimately decides could determine the fate of rail on Oahu. After Thursday’s hearing, Honolulu Corporation Counsel Donna Leong told reporters that it would too expensive and therefore "impossible" to build the elevated rail system if it has to use the alternate route, known as the Beretania Street Tunnel Alternative. That route would go under Aala Park and resurface past Punchbowl Street, then follow King Street and finally head mauka on University Avenue toward the UH-Manoa campus.

It would also cost an additional $960 million to establish a rail route to the Manoa campus instead of Ala Moana Center, rail officials estimate.

But Honolulutraffic.com attorney Nicholas Yost told Tashima that weighing costs of going to UH to a route that ends at Ala Moana Center is an "apples-to-oranges" comparison.

An more accurate comparison, Yost said, would be to compare two routes ending at UH. He suggested comparing the cost of the Beretania alternative to the city’s chosen route to Ala Moana Center — plus a leg extending to UH.

Tashima appeared to agree, saying a system that ended at UH was "the purpose of the project" and that the costs that rail officials highlighted were not a "proper comparison."

Attorneys for the rail project maintained that the Beretania alternative would harm more historic buildings in town than a route running along Nimitz Highway in the Chinatown area.

The Beretania alternative, rail attorney Robert Thornton told Tashima, would affect 47 historic properties. Those include five properties that are either eligible for or listed on the National Register of Historic Properties, according to the city’s supplemental environmental impact statement analyzing the alternative route.

Places on the historic register that would be affected include McKinley High School, Church of the Crossroads and Thomas Square, according to that report.

Thornton and Yost spent much of Thursday’s two-hour hearing debating whether McKinley High buildings would actually be harmed by the Beretania alternative or whether the impact would be limited to a patch of land on the campus where a station would be constructed.

Rail officials are hoping for an expedited ruling. The project could be delayed if they don’t get a favorable ruling by early spring, they say, because of the order Tashima has in place blocking most construction and property acquisition in the heart of town.

Tashima seemed to be aware of the time issues Thursday, saying he would decide "as soon as I can."

Honolulutraffic.com members include former Gov. Ben Cayetano, UH law professor Randall Roth and longtime rail opponent Cliff Slater.

"I think it’s a pretty close case," Cayetano said after the hearing. Roth added that he remains "guardedly optimistic" his group will prevail. The coalition says it has spent some $1 million trying to stop the project in court.

Meanwhile, the city reported last October spending about $5 million combined for outside and in-house attorneys to fight legal battles against rail in state and federal court.

A panel of 9th U.S. Circuit Court of Appeals judges heard arguments in August in San Francisco for the same federal court case. The three-panel judge spent much of that event weighing whether they had jurisdiction, because Tashima’s order had not yet been resolved. A decision from those appellate judges has yet to be released.