BART workers went on strike early Monday after labor talks Sunday evening failed to produce a contract.
Union workers held a press conference at midnight to announce their members would walk off the job on Monday morning.
One union leader said she was "deeply disappointed it has come to this."
Another union representative said BART management "never intended to negotiate a contract with us fairly and squarely."
Patch has posted a survival guide for BART riders with transportation alternatives.
Negotiations had resumed at 3:30 p.m. Sunday, but union representatives left the talks about 8:30 p.m.
BART spokesman Rick Rice said BART has made a "fair offer" that includes an 8 percent pay raise over four years.
“We have a long way to go, but we can’t get any closer if we aren’t at the table," said Rice. "We reached tentative agreements on 11 items today and we should use that momentum to reach a deal. Walking away doesn’t do any good."
However, union leaders said the management proposal fell far short. They pointed out their members had not had a pay raise in four years and had given up $100 million in concessions since the last contract was signed in 2009.
The unions had asked Gov. Jerry Brown to impose a 60-day cooling off period, but the governor on Sunday afternoon said he wouldn't grant the request at this time.
Overnight, BART closed and secured all their stations to protect their property.
BART police will continue to patrol the stations. The 24-hour command center will also remain open.
BART will continue to do inspections on their tracks. Trains running during the strike are making inspections. They'll be operated by trained managers.
The parking lots at 33 BART stations will remain open. They'll be free for carpools and other uses. However, elevators at those lots will not be in operation.
Passengers at so-called joint-use stations will be able to access other transportation services. That includes Muni in four San Francisco stations and Amtrak trains at the Richmond station.
BART is paying for 58 charter buses to pick up San Francisco-bound commuters at four stations -- Walnut Creek, East Dublin-Pleasanton, El Cerrito del Norte and Fremont.
The buses will be able to handle 2,000 to 4,000 people in each direction each day. They're available in the East Bay from 5 a.m. to 9 a.m. and in San Francisco from 3 p.m. to 7 p.m.
Passengers will need to transfer to another bus at the West Oakland station. Commuters will not be able to catch a bus at that station without transferring from another bus.
Ironically, BART set a ridership record for a Sunday this weekend. The transit trains carried more than 276,000 people on the day before the strike. The Gay Pride festivities in San Francisco were the prime reason for the high level of ridership.
BART had extra trains running and extra police officers on duty. The transit district thanked its employees for making the service possible.
It appears union workers at AC Transit will not be on strike on Monday. Their contract also expired at midnight Sunday, but union leaders said in a Facebook post on Sunday evening they would negotiate until midnight and also give the public 24 hours notice before a strike.
Also on Monday, California's gasoline tax increases by 3.5 cents, so people who are driving instead of taking BART will pay a little extra at the pump.