BART and its unions on Friday headed into the final weekend of negotiations as anxious transit riders and freeway drivers were left with no sign they would avoid another round of commuter chaos come Monday morning.

Capping another tumultuous week, both sides in the ongoing labor strife remained far apart late Friday following another daylong negotiating session. The talks, aided by top state and federal mediators, took on a renewed sense of urgency after unions a day before filed their official 72-hour notice of an impending strike. But a breakthrough did not appear imminent.

Earlier in the day, during a special BART Board of Directors meeting, union leaders again blasted BART officials, and the agency's top official responded at a news conference by urging patience.

Jim Allison BART spokesperson speaks during a news conference at BART headquarters in Oakland, Calif., on Thursday, Aug. 1, 2013. BART and its workers
Jim Allison BART spokesperson speaks during a news conference at BART headquarters in Oakland, Calif., on Thursday, Aug. 1, 2013. BART and its workers continue to negotiate towards a new contract as a Monday deadline to strike approaches. (Anda Chu/Bay Area News Group) ( ANDA CHU )

"I want you to know that we are working very hard at the table with our unions trying to get a good deal for the unions and for the system," BART General Manager Grace Crunican said. "I know our riders are incredibly anxious about Monday, as are we, and we are trying our darnedest to make sure we have an agreement and that we have service on Monday."

The 30-day deal that ended the first BART strike a month ago expires at 11:59 p.m. Sunday, and leaders from labor and management were set to bargain throughout the weekend. BART is hopeful that if the two sides make some progress, the unions would decide to continue working under their old contract to keep the trains running.

The stakes are high for each side. An analysis by this newspaper of BART payroll data shows that each day the rail line is shut down, the average blue-collar union worker at BART loses $230 in base pay, plus the chance for large overtime checks. Each day the transit system is out of operation, the agency -- which is partially taxpayer-funded -- has a net loss of $560,000.

While BART's 2,300 blue-collar union workers have not had a raise in four years, they make $76,500 annually on average in gross pay -- easily the most among California transit workers -- do not contribute toward their pension, and pay a flat $92 monthly for medical insurance. Earlier in the week, when both sides openly discussed their latest deals, they were far apart on all three key issues.

City leaders in San Francisco, led by Mayor Ed Lee, joined California Labor Secretary Marty Morgenstern at a news conference at City Hall. They did not take sides as they urged the parties to reach a deal.

Morgenstern, sharing Gov. Jerry Brown's concerns and saying that the governor has been kept up to speed on negotiations, said lack of an agreement would be "a failure" for leaders from both sides. Brown has yet to weigh in on whether he will use his power to order a 60-day cooling-off period, a strategy used by previous administrations to delay strikes.

"The governor will consider all his options," Morgenstern said. "We don't think the whole people of the Bay Area should be kept on pins and needles forever. It's time for this to end."

The Bay Area Council business group, which supports management, released a poll it commissioned that showed 70 percent of respondents opposed the strike, while 30 percent supported it. The poll showed 53 percent of adults thought BART workers were overcompensated, and 16 percent said they were undercompensated.

A poll released by KPIX-TV found management had made a better case than unions by a 2-to-1 ratio, though 29 percent thought neither side had made a good case.

The results of each survey echoed similar, mostly unscientific polls taken during the last strike.

Around lunch time, faith and civil rights leaders came out to negotiations headquarters in Oakland to voice their support for BART workers and deride what they called a smear campaign launched on unions by management. Union leaders attended the news conference but declined to comment.

"We believe it is not too late to avert a strike," said Brian Woodson, pastor of the Bay Area Christian Connection. "The hours we have left are enough to successfully negotiate the issues that are left on the table."

Unions members and supporters of BART workers cheer as union leaders and community members speak during a rally at Frank Ogawa Plaza in Oakland, Calif., on
Unions members and supporters of BART workers cheer as union leaders and community members speak during a rally at Frank Ogawa Plaza in Oakland, Calif., on Thursday, Aug. 1, 2013. (Ray Chavez/Bay Area News Group) ( RAY CHAVEZ )

Staff writer Daniel J. Willis contributed to this report. Contact Mike Rosenberg at mrosenberg@mercurynews.com or 408-920-5705. Follow him at twitter.com/RosenbergMerc.