OAKLAND, Calif. » Commuters in the San Francisco Bay Area got up before dawn on today and endured heavy traffic on roadways, as workers for the region’s largest transit system walked off the job for the second time in four months.

People were lined up well before 5 a.m. today at a Bay Area Rapid Transit train station in Walnut Creek for one of the charter buses BART was running into San Francisco. And traffic at the San Francisco-Oakland Bay Bridge toll plaza into San Francisco and the roads leading to it was backed up for miles.

At the West Oakland BART station, a frazzled Tatiana Marriott raced to board a free charter bus to San Francisco shortly after 6 a.m. She had to be at work by 7 a.m.

"I probably should’ve gotten up a half-hour earlier," Marriott, 21, a seamstress, said, conceding that she would be late for work. "I just want BART and the unions to figure it out. I just want to get to work."

Other alternatives to BART include ferries and Alameda-Contra Costa Transit District buses.

"It’s very frustrating," said Mary Nelson, a retail worker, as she waited for a ferry in Oakland. "I feel like they should be able to come to an agreement. I don’t understand why they’re holding a lot of hardworking people hostage."

The walkout began at midnight Thursday, the culmination of six months of on-again, off-again talks that fell apart. BART and the unions came "extremely close" to agreement on economic, health care and pension issues, but the parties were far apart on work rule issues, said Roxanne Sanchez, president of Service Employees International Union Local 1021.

The impasse came after a marathon negotiating session with the participation of federal mediators.

About 400,000 riders take BART every weekday on the nation’s fifth-largest commuter rail system. The system carries passengers from the farthest reaches of the densely populated eastern suburbs to San Francisco International Airport across the bay.

SEIU said it was fighting to prevent BART from changing employees’ fixed work schedules. Some employees work four-day, 10-hour shifts while others work five-day, eight-hour shifts. Union officials said BART wanted to schedule people as they saw fit.

BART officials say work rules refer to past practices that require approval from unions and management to change. The rules make it difficult to implement technological changes or add extra service on holidays because of a special event, the agency says.

Sanchez said SEIU and the Amalgamated Transit Union suggested taking the remaining issues to arbitration but management refused.

BART General Manager Grace Crunican countered that the agency needed to alter some of those rules to run the system efficiently. She said BART also needed to control costs to help pay for new rail cars and other improvements.

"We are not going to agree to something we can’t afford. We have to protect the aging system for our workers and the public," Crunican said.

She urged the union leaders to let their members vote on management’s offer by Oct. 27.

A four-day strike in July saw commuters lining up early in the morning for BART’s charter buses and ferries across the bay, and enduring heavy rush-hour traffic.

The San Francisco Municipal Transportation Agency said it has developed plans to help people to get around, including providing two expanded carpool locations.

The key issues during most of the talks had been salaries and worker contributions to their health and pension plans.

Talks began in April, three months before the June 30 contract expirations. The unions initially asked for 23.2 percent in raises over three years. BART countered with a four-year contract with 1 percent raises contingent on the agency meeting economic goals.

The unions contended that members made $100 million in concessions when they agreed to a deal in 2009 as BART faced a $310 million deficit. And they said they wanted their members to get their share of a $125 million operating surplus produced through increased ridership.

On Sunday, BART negotiators presented a final offer that includes an annual 3 percent raise over four years and requires workers to contribute 4 percent toward their pension and 9.5 percent toward medical benefits.

The value of BART’s proposal is $57 million, BART spokeswoman Alicia Trost said.

Workers represented by the two unions, including more than 2,300 mechanics, custodians, station agents, train operators and clerical staff, now average about $71,000 in base salary and $11,000 in overtime annually, the transit agency said. BART workers currently pay $92 a month for health care and contribute nothing toward their pensions.

Associated Press writer Haven Daley contributed to this report.