Local trains are not running because of an Amtrak power breakdown which has in turn shut down SEPTA train lines in the Philadelphia area as well as on the New Jersey transit system.
Naturally, infuriated commuters who were stranded on the trains wanted to get off and find other means of transportation to work.
But according to Reuters, they were threatened with arrest:

New Jersey Transit said the outage halted its two most heavily traveled lines, which move 70,000 passengers per weekday, and some trains destined for midtown Manhattan have been diverted to Hoboken, New Jersey, across the Hudson River from New York.
“It just stopped,” said public relations executive Liz Anklow, stuck on a New Jersey Transit train for two hours. “It started to get very hot in there” before railroad workers opened doors for ventilation.
“A very imposing New Jersey trooper just walked through the train and said if one person leaves the train you will be arrested and taken to jail,” Anklow said.

I’d like to know just what the charge would be. Trespassing, perhaps? I don’t see how that would hold up, because the intent is not to trespass, but to leave.
Legally, when people are compelled to remain in a certain place by force, that constitutes the tort of false imprisonment. The airlines understand this, which is why passengers are allowed to leave grounded or stranded planes when that is possible.
It happened to me once when a flight I took to San Francisco was forced to land in Oakland because of problems with the San Francisco airport. The flight crew tried to stop passengers from getting off the plane, but after someone conferred with the airline’s uppity-ups, they announced that passengers would be allowed to leave “but we cannot guarantee your safety in Oakland.” Fine with me, as I never wanted a safety guarantee, so I left.
Absent a life-threatening emergency or something, I don’t think New Jersey Transit had any right to hold people against their will, and unless there’s no tort of false imprisonment in New Jersey, I think they can sue.
(Unless the freedom thing is a loophole or something. . . )
MORE: In a report after the power was restored, I see that at least some pasengers managed to get out while avoiding arrest:

NEWARK, N.J. (AP) — A major power outage stranded thousands of rush-hour commuters Thursday between New York and Washington, stopping trains inside sweltering tunnels and forcing many passengers to get out and walk.
Power was restored throughout the heavily traveled corridor at about 10:30 a.m., more than two hours after outage, Amtrak said.
The outage stranded five trains in tunnels – one in Baltimore and four under the Hudson River heading into New York. The last one lurched back to life at 11:15 a.m. after stranding passengers for more than three hours in the heat and darkness.

Such defiance should have been met with a SWAT team!