The crew detected an odor in the first car just before 6:45 a.m. and asked passengers to move into the other cars. When the crew did not see anything that warranted further action and continued on to 30th Street Station, said Jim Jordan, assistant general manager for public safety.
About a mile from the station, the engineer noticed smoke and then flames. The three crew members then helped evacuate about 500 passengers through the doors and emergency windows, Jordan said.
SEPTA also evacuated about 500 people that were on a train that was on an adjacent track.
There were no reports of serious injuries.
The rail car, which went into service in 1965, was completely destroyed within minutes. It is the first time a blaze has completely engulfed a SEPTA vehicle, said Joseph Casey, SEPTA general manager.
SEPTA spokeswoman Jerri Williams said the fire started either in a heater or a traction motor.
"I can tell you there is absolutely no indication it is strike related," said SEPTA spokeswoman Jerria Williams.
Alicia Boyd, 40, a data entry clerk, got on the first car of the train in Overbrook.
"It was smoking when we got on," she said. "It smelled like burning rubber."
Before the train pulled out of the station, passengers in the first car were moved to the back of the train before it burst into flames, SEPTA officials said.
The train then stopped and all the passengers on the train got off, Boyd said.
"The whole front car was black and melting," she said, adding that flames leaped out of the windows. "It was incredible."
Service on the R5 and R6 Cynwyd lines was suspended west of Suburban Station for two hours because of the blaze. The fire also disrupted Amtrak service between Philadelphia and Harrisburg until 8:30 a.m.
The city's Office of Emergency Management arranged for school buses to transport stranded passengers to Suburban Station.
Heather Durkee of the city's Overbrook Farms section was the last passenger to board the ill-fated R5 train at the Overbrook station.
"I went running through to tunnel to get onto to the train," said Durkee, who teaches design at the Charter High School for Architecture and Design in Center City.
The conductor urged her to hurry because the train was about to leave. Durkee scrambled aboard the last car and found herself standing next to the conductor who was holding his walkie-talkie.
As the train pulled out, she felt it lurching repeatedly. "I thought 'that's weird. But there's a huge amount of people on this train. Maybe the bodies are making it do that,'" Durkee said.
Then she detected an odd odor.
"All of a sudden it smelled funny," she said. "You could smell this burning of brakes or whatever . . .. And then all of a sudden the train stops. And then I heard on the walkie talkie: 'Overbrook station. Overbrook station. Fire and smoke. Fire and smoke'."
Durkee got off without incident, and saw a car up front on fire.
"There were literally billows of smoke coming out and flames," she said.
She saw some passengers jumping out of windows.
Durkee found one of her colleagues, Andrew Phillips of Narberth, in the train stopped behind hers. When they learned no trains would be moving for some time, Durkee called her husband who works in Center City.
Phillips used the GPS on his Apple iPhone to figure out their location, and they walked to a Lowe's at Lancaster Avenue and 52nd Street where Durkee's husband picked them up. They arrived at the charter school at 6th and Sansom Streets shortly at 8:45 a.m.
Peter Kim, 39, of East Fallowfield, who was headed to work at Independence Blue Cross, was in the second car.
"The smoke started coming into the second car," he said. "The biggest issue I had was the conductor walked by and no one told us to get off."
Jim Cade, 61, was at work at his auto body shop on Lancaster Avenue, when he heard noise and commotion outside his building.
He said he saw an "ocean of fire trucks," flames and smoke pouring from the train, and dazed passengers with their "briefcases, suits and high heels" making their way down the track.
The scene looked like part of a disaster movie, Cade said.
The passengers "were more so in bewilderment of what to do," said Cade. "Nobody was hysterical. Everyone was peaceful."
He said many were already on cell phones trying to figure out what to do next and how to get to work or back home.
"They were half way to nowhere," he said.
Contact staff writer Mari A. Schaefer at 610-892-9149 or firstname.lastname@example.org.
Staff writer Sam Wood contributed to this story.