PROVIDENCE — The state’s bus system, already in serious financial trouble that could force major service cuts, is headed for worse, according to projections by the Rhode Island Public Transit Authority.

In a presentation for the Governor’s Blue Ribbon Panel on Transportation Funding, RIPTA Assistant General Manager Mark Therrien said the authority expects its deficit, estimated at $12 million this fiscal year, to keep growing, doubling in four years.

The governor’s panel is grappling with a pair of transportation financing crises. Its focus so far has been on the state’s highways and particularly its bridges, which are failing and need repairs costing hundreds of millions of dollars, according to the state Department of Transportation.

RIPTA’s problem is different: how to pay its drivers and mechanics and buy expensive diesel fuel to run the buses. Its revenue continues to fall behind its expenses, officials have said, because of the run-up in the price of fuel coupled with the failure of the state gasoline tax to produce enough money.

RIPTA’s deficit this year, including a $2-million shortfall carried forward from the past fiscal year, would amount to 12 percent of the authority’s budget.

The RIPTA board of directors has adopted a $101-million budget for this fiscal year, but that is $12 million more than the authority’s expected revenues. The board has not said what it will do about that deficit. It has before it a service cutback plan that would affect more than 160 bus lines or parts of lines to save $9.7 million.

Speaking to the governor’s panel on Thursday, Therrien told the members that revenue from passengers makes up only 29 percent of RIPTA’s budget and that the panel can’t expect the authority to ever break even.

“Transit does not make money,” he said. “Everybody loses money,” he said, referring to other public transit agencies.

He said that while some routes make money, the average cost per passenger is $3.15. RIPTA’s base fare is $1.75 per ride and it offers discounts from that for multiple rides.

Therrien gave another example of the size of the subsidies supporting RIPTA’s fares, service for people with disabilities that he described as “very expensive.”

People with disabilities who can’t use the authority’s conventional buses and who live within three-quarters of a mile of RIPTA’s fixed bus routes can use its paratransit buses, paying $3.50 per trip each way, no matter how long the trip is. Therrien said the fare pays only 7 percent of the actual cost of delivering the service.

“There’s no magic in it,” Therrien said. “You’ve got to have the subsidy.”

Meanwhile, some RIPTA buses continue to pass up would-be passengers because the buses are full, and the authority, considering a major service reduction to save money, can’t afford to increase service.

Therrien said it would take 30 more buses and another $3 million to cover operating expenses to reduce crowding. He said the reduction of transportation benefits to many members of the state’s RIte Care health-insurance program, ordered by federal Medicaid officials, could reduce crowding on some buses. However, the change will also cost RIPTA millions of dollars per year that it has been paid by the state Department of Health and Human Services.

For the Blue Ribbon Panel, co-chairman Jerome F. Williams said, “It is getting to be crunch time.”

The panel’s schedule has it making recommendations on how to address the state’s transportation funding crisis by early November.

So far, it hasn’t indicated publicly what it will recommend to the governor. But a ready source of huge amounts of money that wouldn’t cause an outcry isn’t obvious, and some of the possibilities mentioned, including tolls on major highways, would probably be controversial.

Williams said the panel will hold hearings early next month around the state to see what the public thinks.

In the meantime, John Simmons, who is also executive director of the Rhode Island Public Expenditures Council, a business group, said it’s not clear what the public makes of the situation.

“The public may not know there’s a real problem,” he said.

Another member, Kazem Farhoumand, acting chief engineer of the DOT, wondered how the public would react if the commission ends up with a number of possible but unappealing revenue sources, such as a higher gasoline tax or tolls.

“What if everything is ‘No’?” he asked. “What do we do now?”

blandis@projo.com