Isolated events - substation failures, even a single downed tree - have repeatedly stopped the entire Northeast Corridor, a railroad network that is called on to move tens of thousands of people daily through the nation's densest population centers.
Amtrak said low-voltage troubles forced it to suspend service between New York City and Washington, and between Philadelphia and Harrisburg, Pa., starting at 7:45 a.m. Power was restored around 9 a.m.
The exact cause wasn't immediately known, but Amtrak spokeswoman Karina Romero said the problem was more widespread than usual. Amtrak was focusing its investigation on the area between Washington and Perryville, Md., Romero said.
Railroad advocate Ken Briers said such troubles are not necessarily the sign of an antiquated, decrepit or underfunded system. Service interruptions today are more likely the result of software glitches or tweaks to a system that Amtrak is actually upgrading, said Briers, a former train operator and director of the National Association of Railroad Passengers.
Amtrak has embarked on a long-term program to modernize dozens of substations along the Northeast Corridor, some of which date to before World War II.
"One of the negatives about an electrified railroad is if anything happens, it's never minor," Briers said. "I think they're moving in the right direction with this system to improve the control with the power supply. But I think there's a learning curve here, and you've got no place to practice, except on your own system."
Briers stressed that he didn't know what caused Tuesday's outage, but said low-voltage problems are often the result of a surge-protector kicking in because of a power surge or other reason.
Amtrak has experienced similar electrical malfunctions in the past, spotlighting problems with the railroad's aging Northeast power-supply system.
A low-voltage problem brought train service to a standstill two days before Christmas in 2009, snarling train traffic along the East Coast for thousands of commuters and holiday travelers.
In May 2006, a faulty control at a single substation improperly restricted power, causing a power outage that shut down the corridor and stranded some passengers in hot tunnels.
Two weeks ago, a tree fell on wires near Hamilton, N.J., knocking out power and rail signals and bringing the corridor to a halt.
Snarled rail commutes haven't been restricted to Amtrak lines in recent days. On Monday, a 90-year-old pneumatic switching system for the Long Island Railroad in suburban New York was damaged in a fire that might have been sparked by an electrical short brought on by heavy rain.
Problems have become so common throughout the rail-dependent region that some commuters shrug them off.
"I'm frustrated, but I'm kind of used to it by now," said Arad Shaiber, a 30-year-old software engineer from Philadelphia who was trying to get to work in Downingtown, Pa.
The outages are sometimes local, other times widespread, but always frustrating.
Robinson Rivas moved from New York to Philadelphia three months ago and takes the train to his job at a pharmaceutical company in the suburbs. He pondered whether to try to take a cab to work, which he estimated would cost him $100.
"I was a happy commuter until now. Now I realize how vulnerable, you know, my commute can be," he said. "This changed in the drop of a hat and I don't even have any alternate plans."
Amtrak said about 30 of its trains were affected by Tuesday's outage. It was trying to tally the numbers of passengers impacted by the delays. Service had been fully restored by Tuesday evening's rush hour.
The problems also forced NJ Transit, the Southeastern Pennsylvania Transportation Authority and Maryland Transit Administration, which run on rail lines operated by Amtrak, to halt their trains. The stoppage caused residual delays throughout the day.
Harold Kirsten, 60, of Avon, Conn., had to stay overnight in Philadelphia because storms canceled his flight Monday evening, and was having a tough time leaving Tuesday morning because of the train delays. He was trying to make his way to Newark, N.J., for a business meeting.
"You learn over time to adapt, otherwise you'll have a nervous breakdown," he said as he read a book on his iPad to pass the time.
Barbara Strudler, of New York City, met her 12-year-old granddaughter, Fay Smulowitz, at the Trenton, N.J., station to embark on a three-day tour of Baltimore.
"I'm glad I brought some food," Strudler said once she noticed the 90-minute delays.
On Long Island, the railroad stopped service for several hours and was running on limited service Tuesday as it worked to fix the damage from the switching station fire. The LIRR said it could take several days to make repairs. The system is due for a $60 million overhaul this fall.
Contributing to this report were Associated Press writers Randy Pennell, Patrick Walters and Erin Vanderberg in Philadelphia; Deepti Hajela in New York City; Frank Eltman in Garden City, N.Y.; Beth DeFalco in Trenton, N.J.; and Jessica Gresko in Washington.