OAKLAND, California (AP) — Hundreds of thousands of commuters in the San Francisco Bay area clogged highways, swarmed buses and shivered on ferry decks Friday as workers for the region's largest transit system walked off the job for the second time in four months.

The strike could drag through the weekend and into next work week. Bay Area Rapid Transit spokesman Rick Rice said that no new talks have been scheduled, and representatives from the unions were meeting and didn't immediately return calls from The Associated Press.

Discussions fell apart late Thursday after a marathon 30-hour negotiation with a federal mediator that put representatives from both sides at dueling press conferences, rumpled, unshaven and angry.

Six months of on-again, off-again negotiations have brought agreement on key issues such as raises, health care and pensions. But there remained a snarl Friday: a package of work rules involving when schedules are posted, whether workers can file for overtime when they've been out sick, and how paychecks are delivered.

The BART system carries about 400,000 workers a day through tunnels under the bay and into the region's urban core of San Francisco from four surrounding counties, relieving what would otherwise be congested bridges.

In an effort to alleviate delays, many of the Bay Area's other 27 transit systems added bus, ferry and rail service Friday. Carpools and rideshare programs were also busy, and more cyclists took the streets.

But traffic was sluggish all morning, and lines at bridge toll plazas were backed up for miles (kilometers).

Passengers touching down at San Francisco International Airport were warned that trains weren't running, and it could take twice as long to get into the city.

Many simply avoided the hassle, telecommuting instead.

Talks started in April, two months before the June 30 contract expirations, but both sides were far apart. 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.

But the transit agency countered that it needed to control costs to help pay for new rail cars and other improvements.

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Associated Press writers Martha Mendoza and Haven Daley contributed to this report.