On Saturday, the two sides met separately for most of the day and then held an evening bargaining session that broke off at 11 p.m. PDT.
No details on Saturday's session were released, at the mediator's request. Representatives emerged from the talks saying they had made progress, but also that much work remained before a contract agreement could be submitted to union members.
Trost said BART was preparing to offer riders free trips from the East Bay to San Francisco on buses if a strike occurs. She also said a dozen managers have been certified to operate BART trains, but the transit agency isn't planning to use them immediately. She said the BART board of directors would have to approve the use of managers as train operators.
"The board would need to decide if they want BART to operate limited train service by managers," Trost said. "That isn't the plan right now."
Amalgamated Transit Union Local 1555 and Service Employees International Union local 1021 want a raise of nearly 12 percent over three years, while BART has proposed a 10 percent increase over four years. BART said workers from the two unions now average about $71,000 in base salary and $11,000 in overtime annually.