A Bay Area Rapid Transit train leaves the station Tuesday, Oct. 15, 2013, in Oakland, Calif. A recipe for gridlock was brewing in the San Francisco Bay Area, as two of the region's major transit agencies teetered on the brink of commute-crippling strikes. While talks between the Bay Area Rapid Transit agency and its unions to avoid the second walk-off in four months were set to resume on Tuesday, workers at a major regional bus line said they would go on strike in 72 hours. Bay Area Rapid Transit passengers wait to board a train Tuesday, Oct. 15, 2013, in Oakland, Calif. A Bay Area Rapid Transit train arrives at a station Tuesday, Oct. 15, 2013, in Oakland, Calif. A passenger rides a Bay Area Rapid Transit train Tuesday, Oct. 15, 2013, in Oakland, Calif. (AP) - The San Francisco Bay Area's main commuter rail line was up and running Wednesday as a potential transit strike was averted for the third straight day. The Bay Area Rapid Transit agency and two of its largest unions have made some progress in the intense negotiations to avoid a second strike in more than three months, Federal mediator George Cohen said late Tuesday. Negotiations will resume Wednesday, just hours after another marathon session Tuesday ended shortly after midnight, the Service Employees International Union Local 1021 said Wednesday. "We truly understand the riders' frustration, because we share the same frustration that we've not yet reached an agreement," SEIU 1021 president Roxanne Sanchez said. We are encouraged by the progress we've achieved, and at the request of the federal mediators, we will continue to bargain. BART is the nation's fifth-largest rail system and the threat of another strike would likely cripple the morning commute has been looming over riders who have already endured at least a half-dozen strike deadlines from the SEIU and the Amalgamated Transit Union Local 1555. Meanwhile, workers at the Alameda-Contra Costa Transit District, a major regional bus line, have also threatened to strike this week if their conditions for a new contract aren't met. Hundreds of thousands of commuters in cities like Oakland and Berkeley depend on the two transit systems and roadways would be further congested if the strikes coincide. AC Transit which serves about 100,000 riders mostly across the East Bay also has buses shuttling to and from San Francisco. The buses served as an alternative for many BART train riders during a nearly five-day strike in July. The bus workers issued a 72-hour strike notice Monday with plans to walk off on Thursday. On Tuesday, the AC Transit board requested that Gov. Jerry Brown impose a 60-day cooling off period. The board said a bus strike would significantly endanger the public's health, safety and welfare. AC Transit and BART union officials deny any coordination. Still, the specter of both transit agencies striking simultaneously could give them leverage if the governor doesn't delay the bus workers strike. Sticking points in the 6-month-old BART negotiations include salaries and workers' contributions to their health and pension plans. BART officials confirmed Tuesday that some progress has been made but economic issues still need to be hammered out. BART General Manager Grace Crunican presented a "last, best and final offer" Sunday 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 over four years and that figure also includes money for smaller unions and nonunion workers, BART spokeswoman Alicia Trost said. BART is looking at the unions' counterproposal and trying to see how they could possibly fit into management's final offer, Trost said. "Everyone's working very hard," Trost told reporters Tuesday. The general manager's there, she's meeting with the federal mediator. He's still going between both (parties) floors to see if we can come to a deal. SEIU Local 1021 executive director Pete Castelli said Monday the parties were somewhere between $6 million to $10 million apart over four years. ATU President Antonette Bryant told reporters Tuesday the union would not discuss any details of the talks because of a gag order imposed by the mediator. "We're not trying to avoid, mislead or keep information to ourselves," Bryant said. We are diligently working trying to get a contract for our members and to get the riding public held off hostage.