SEPTA's biggest labor contract expires Friday night, but an immediate strike by Philadelphia bus drivers, subway and trolley operators, and maintenance workers seems unlikely.

Negotiations between SEPTA and union representatives continued Wednesday at the Sheraton Philadelphia Downtown Hotel.

The contract with Transport Workers Union Local 234 covers about 4,700 SEPTA employees in the city, roughly half of all the transit agency's workers.

Separate contracts expire next month with TWU 234, Suburban Transit Division, Victory District, which represents about 160 suburban maintenance and clerical employees; and TWU 234, Suburban Transit Division, Frontier District, which represents about 230 bus drivers and mechanics in Montgomery and Bucks Counties.

Also expiring in April is a contract with members of United Transportation Union Local 1594, Suburban Transit Division, Victory District, which represents about 360 operators on the Media/Sharon Hill trolley lines and conductors and operators on the Norristown High-Speed Line.

Although TWU leaders have alerted their members to prepare for a strike, a walkout seems unlikely before the suburban contracts expire in April.

And so far, no strike-authorization vote has been taken by the TWU's members.

In the event of a strike, Regional Rail trains would continue to operate because their crews are covered by separate contracts. Train engineers have been working without renewed contracts since 2010.

Typically, any agreement reached by TWU 234 for its city workers sets the pattern for SEPTA's 16 other labor contracts.

The TWU last went on strike in 2009, seven months after its contract expired.

That surprise predawn walkout left thousands of commuters in the lurch, drawing fire from Mayor Nutter and then-Gov. Ed Rendell. The strike lasted six days.

The TWU had threatened to strike as the World Series was being played in Philadelphia, but it did not actually go out until 3 a.m. Nov. 3, after the series left town.

Union president Willie Brown said at the time, "I understand I'm the most hated man in Philadelphia right now. I have no problem with that."

Brown, who lost his bid for reelection in 2010 to John Johnson Jr., defeated Johnson in voting in September to regain the presidency of Local 234. He is leading the negotiations with SEPTA.

The base salary for new SEPTA bus drivers is $33,887, and drivers with four or more years of experience are paid $55,620 a year. Including overtime pay, the typical TWU member makes $64,847 a year, SEPTA spokeswoman Jerri Williams said.

"Whether or not there is a strike is in the union's court," Williams said. "SEPTA management remains ready to address the issues and explore common solutions, and we are hopeful that good-faith negotiations will eventually result in a contract."

Jamie Horwitz, a spokesman for the TWU, said Brown "is committed to getting a fair settlement for his members," but declined to specify the issues that stood in the way of a settlement.