On behalf of Corbett, Pennsylvania transportation secretary Barry Schoch called both sides Friday to seek a two-week delay in any work stoppage and to urge them to reach a settlement.
A top-level official from the National Mediation Board met with representatives of SEPTA and the unions shortly before 8 p.m. in the Center City law offices where the two sides met with another NMB mediator earlier in the day, to no avail.
Passengers scurrying to catch the last trains of the night were relieved to find that all runs were being completed before the trains were parked in the yards and the engineers officially walked off the jobs.
Union leaders said pickets would immediately be posted at the rail yards and employee entrances at some stations.
Of the decision to strike, SEPTA spokeswoman Jerri Williams said, "We're disappointed."
"We made an offer of a two-week extension, and so did the governor's office, but it was rejected."
"We regret the inconvenience."
She urged riders to check SEPTA's Web page at http://septa.org/service/service-interruption/rail.html for alternate service options.
SEPTA will add service during non-peak hours on bus, subway and trolley routes and the Norristown High-Speed Line. No additional vehicles or employees are available during peak hours, Williams said.
SEPTA will not ask Obama to create an emergency board and order the strikers back to work, she said.
Stephen Bruno, vice president of the Brotherhood of Locomotive Engineers and Trainmen, also expressed regret that riders now face a work stoppage.
"We gave it the best effort we could," Bruno said after talks ended. "A resolution was available - binding arbitration is a viable option."
Both the BLET and IBEW Local 744 offered to submit their labor dispute to binding arbitration. SEPTA declined arbitration, saying it believed it could get better terms through negotiation.
Corbett could move as early as Saturday to request a president emergency board.
"The governor's primary concern is for the riders of Southeastern Pennsylvania to have the ability to get to their jobs or shopping or wherever they need to go," Corbett's press secretary, Jay Pagni, said Friday. "Both parties should keep the riders foremost in their consideration."
It remained unclear how quickly a board could be appointed and how long the rail workers might remain off the job if Obama creates a board.
Before the strike, Mayor Nutter said his office was monitoring the talks and hoping for the best.
"We hope SEPTA management and the unions can work out their differences and avoid a shutdown," Nutter spokesman Mark McDonald said Friday.
A strike "will be very, very inconvenient for people who rely on Regional Rail," said Tony DeSantis, president of the Delaware Valley Association of Rail Passengers. "Particularly in places like Bucks County, there is no good alternative."
"But it may not last very long. . . . It really depends on who is willing to accept a long strike to get what they want."
The members of the two rail unions have been working for years without new contracts - the International Brotherhood of Electrical Workers (IBEW) since 2009 and the Brotherhood of Locomotive Engineers and Trainmen (BLET) since 2010.
Other rail workers, such as conductors and assistant conductors, are not on strike and will continue to report for work and be paid. They will get other assignments or undergo training, Williams said.
The 220 engineers and 210 electrical workers announced their plans to strike after SEPTA's decision this week to impose management's terms to settle the long-running labor dispute.
SEPTA alerted union officials Monday that it would implement previously offered pay raises, effective Sunday.
The raises are based on the pattern established by the contract settlement in 2009 with SEPTA bus drivers and subway operators represented by Transport Workers Union Local 234.
Those increases would give electrical workers a raise of 11.5 percent Sunday, and the engineers would get a 5 percent raise Sunday and an additional 3.5 percent raise July 6, SEPTA said.
Wages for electrical workers would increase by about $3 to $29.50 an hour, on average. Electrical workers on average earn $55,120 a year, not counting overtime.
The top wage rate for engineers would increase by $2.64 per hour, to about $32.50 an hour. Engineers, who typically work six-day weeks, now earn an average of $95,290 a year, SEPTA said.
The railroad workers have two major objections to the SEPTA offer: They want the raises to be retroactive to the expiration of their last contracts, and they want an additional 3 percent raise, which they say represents the value of a pension benefit increase received by the TWU in 2009. The railroad workers are in a different pension plan from the TWU.
SEPTA general manager Joseph Casey said the pension benefit increase of $4 million a year for the TWU is offset by a higher contribution now paid by the workers. SEPTA maintains there is no cash value from the pension benefit increase.
Talks between SEPTA and the rail workers have been fruitless for years. Federal railroad law requires a lengthy negotiation and mediation process before either side in a passenger rail dispute can resort to "self-help" - a strike or a management lockout. That period was to expire at 12:01 a.m. Saturday.
Although the current dispute involves only Regional Rail service, the contracts for bus drivers, subway operators, mechanics, and cashiers expired this year.
A strike by those workers is also possible on short notice, though no strike-authorization vote has been taken.
TWU Local 234 president Willie Brown said this week that his union, which represents about half of SEPTA's 10,000 employees, would not strike now.
A strike by TWU members at the same time as the rail workers would halt SEPTA's entire system. That has never occurred in SEPTA's 50-year history, and such an action has been held by TWU leaders as the ultimate threat against SEPTA.
The last Regional Rail strike was in 1983, and it lasted 108 days.
Inquirer staff writer Claudia Vargas contributed to this article.