SAN DIEGO — What was heralded in late 2007 as the next big thing in regional commuting — a 10-mile, privately operated toll road in South County — may wind up testing the wisdom of public-private partnerships.

In its court filing this week for Chapter 11 bankruptcy protection, the company that runs the South Bay Expressway cited the ripple effects of a rotten economy. It said the collapse in home prices and the spike in unemployment have hurt its fortunes since the road opened nearly three years ago.

“What’s driving this is that we’ve been severely impacted by the recession,” said Greg Hulsizer, chief executive for South Bay Expressway Ltd. “We find ourselves in a position where in the not-too-distant future, we’re going to run out of financial reserves.”

On average, nearly 22,600 cars travel the road each day, far below initial projections of 60,000. Riders typically marvel at the seemingly empty stretches of pavement, even during peak traffic hours.

While revenue is steady because of rising tolls, the company is falling about $16 million short each year in what it owes its direct lenders, according to court filings.

Monday’s bankruptcy move raises questions about the fate of the tollway and the private-public partnership behind the $843 million project.

South Bay Expressway built the road, and it has a long-term management agreement with Caltrans. When the deal was crafted in 1991, it was lauded as a novel way to finance public roads.

“The idea was to see if the private sector could succeed in building highways,” said Marlon Boarnet, a professor of planning policy and design at the University of California Irvine. “But one thing that history is teaching us is that it is more complicated that we thought.”

Hulsizer said his company intends to operate the tollway through bankruptcy reorganization and beyond, even though he doesn’t expect the venture to turn a profit anytime soon. He hopes a judge will give the business some breathing room by allowing it to restructure its debts, perhaps by lengthening its loan-repayment schedule.

“As a valued customer, you will see no change in service,” he promised drivers in an e-mail yesterday. “Your local toll road will still be here for you.”

In a phone interview, however, Hulsizer said turning over operations to another private business or the company’s lenders may be an option, depending on the outcome of bankruptcy proceedings that could last a year or more.

Many South County commuters said they weren’t surprised by the bankruptcy bid and blamed the operator, saying its decision early last year to boost tolls drove away customers.

Motorists pay $2.50 to $4.50 per trip, depending on length. Those with FasTrak, an electronic tolling device, pay $2 to $3.85, or 75 cents for trips between Birch Road and East H Street.