For six days in July, equipment failures forced New Jersey Transit trains to share a single Hudson River tunnel, delaying Manhattan commuters as long as 90 minutes.

Such disruptions will mount even if Amtrak, the national passenger railroad that owns the century-old tracks, makes repairs and builds replacements, which could take until 2030.

New Jersey Transit’s solution calls for flexible bosses.

In the event of a prolonged shutdown, the agency is counting on about one-third of its more than 165,000 daily Manhattan commuters to work from their houses. About 60,000 would be channeled to ferries and the rest could go by “a robust bus program,” said Nancy Snyder, a spokeswoman. Undetermined is what that would cost, or who would pay for such a workaround.

“This tunnel is going to be harder and harder to keep functioning reliably,” said Stephen Gardner, Amtrak’s executive vice president for Northeast Corridor business development. “It’s unreasonable to expect that there’s not going to be further kinds of disruptions or additional outages needed over several years ahead.”

New Jersey Transit, the nation’s third-largest commuter system, has few options. The ability to cross-honor, or send rail ticketholders to buses and the PATH subway during service interruptions, is constrained by space at the Port Authority terminal in Manhattan.

“For both bus and rail we are at or near full capacity in the peak,” Snyder said in an e-mail. Alternative transportation costs were too difficult to forecast, she said, because “many variables” can affect pricing.

“Amtrak has yet to come up with a plan or schedule regarding tunnel repairs that are expected to take place over the next 20 years,” Snyder said. “Until that happens, New Jersey Transit cannot speculate on the type of alternatives that may be necessary.”

Riders got a preview in 2012, when hurricane damage led to 10 weeks of emergency bus and ferry service that cost the U.S. government $7.53 million.

Paying Already

Last month’s transportation travails came after New Jersey Transit’s board met its current budget with service cuts and a 9 percent fare increase, even after riders at nine public hearings complained bitterly about crowding and unreliable schedules.

The delays led U.S. to Transportation Secretary Anthony Foxx call for meetings with New Jersey Governor Chris Christie and New York Governor Andrew Cuomo to discuss reviving Gateway, an alternative proposed by Amtrak in February 2011. The $16 billion project, which includes replacement of the key Manhattan link on Amtrak’s Washington-to-Boston Northeast Corridor, has languished without financial commitments.

While Amtrak operates as a for-profit corporation, it depends on taxpayer subsidies criticized by some congressional Republicans. By 2020, Amtrak will have just 25 percent of $4 billion needed for planned Northeast Corridor projects.

Electricians are working nights in the Hudson River tunnels to replace 600 feet (180 meters) of copper cable. Yet almost 12 miles of the 80-year-old conduit snake inside the rail tube, which was flooded with corrosive chlorides and sulfates by Hurricane Sandy three years ago.

Last year, Joseph Boardman, chief executive of Amtrak, said the connection has less than 20 years remaining.

“What are we going to do if we have to take one of these tunnels out of service if we have to fix it?” said Loretta Weinberg, a Democrat who is the New Jersey Senate majority leader and vice chairwoman of the chamber’s Legislative Oversight Committee.

She and the panel’s chairman, Senator Bob Gordon, have called an Aug. 10 hearing with top officials from Amtrak, New Jersey Transit and the state transportation department.

Democrats have criticized Christie’s 2010 decision to scuttle an earlier tunnel project, the $12.4 billion Access to the Region’s Core, that would have doubled peak service to Manhattan as soon as 2018.

Standing Room

Christie, a second-term Republican who’s running for president, has said he was displeased by that tunnel’s design and concerned that costs would balloon. He and Cuomo have said they are both willing to discuss Gateway.

Until then, pressure on commuters promises to grow.

In five years, 2 percent of passengers will be seatless between 7:30 a.m. and 8:30 a.m. on their way to New York, even with maximum use of double-decker cars, a planning report shows.

“More buses is the obvious answer,” said Martin Robins, professor emeritus at Rutgers University and the initial ARC project director. It’s not so simple.

A year ago, the Port Authority of New York & New Jersey budgeted $90 million to ease congestion at its 65-year-old New York City bus depot, where a third of boardings are for New Jersey Transit. John Degnan, chairman of the authority’s governing board, says that expenditure enables only temporary fixes for ever-increasing crowds in a crumbling building.

“Could we handle several thousand more commuters a day from the 220,000 trips that are taken a day?” Degnan said. “Yes, but it’s already beyond peak capacity. From a 2020 perspective, the bus terminal is not the answer to the problem of congestion on the rails.”