She said she had no apparent injuries but was "feeling kind of banged up" and had scheduled an appointment with her doctor.
Biswanger, a deputy solicitor for Delaware County, said her biggest concern was, "What if this was happening to somebody even more vulnerable?
"What if I was elderly, or what if I was carrying a baby?"
SEPTA spokeswoman Jerri Williams said Regional Rail policies require conductors to make sure all passengers are safely off trains before the signal is given to engineers to start moving.
"It is absolutely the conductor's responsibility and one of his most important duties to stand on the ground at platform level and watch passengers disembark," Williams said. "He signals the engineer when no passengers are getting on or off the train.
"So if this occurred as she said, it would have been the conductor's fault."
Williams said SEPTA officials were investigating and if the conductor is determined to be at fault, he or she would face discipline, including possible suspension.
Biswanger, who said she had limited use of her arms because of a spinal cord stroke several years ago, said she was returning to Eddystone from Newark, Del., on a train that left Newark at 8:58 a.m. Monday.
SEPTA's daily Train 9220 departs Newark at 8:58 and arrives at Eddystone at 9:37, according to a SEPTA schedule.
Biswanger said she was the only passenger getting off the train at Eddystone and she said she did not see a conductor.
She said she was struggling with her suitcase, still one step from the ground, when she heard the double-beep signal for the engineer to proceed and the train started to move.
"I was sort of in midair. I couldn't go forward or back," she said. "I swung counterclockwise and I ended up in the gravel next to the curb, with the train passing over me. I could see the steel wheels going past my head."
After the train passed, Biswanger rolled onto the platform, dazed and scared. She called Howat, who arrived quickly, as did a local police officer.
"I raced down there, and she was just sitting on the blacktop, crying," Howat said.
Howat said a second SEPTA train stopped at the station and a conductor came down to talk to Biswanger and apparently notified SEPTA police.
"A lot of time at these stations, if they don't see anybody waiting to board, they just kind of slow down," Howat said. "But it's a shame. There's got to be a better way."
Howat said she waited with Biswanger at the hospital until Biswanger's son-in-law came to pick her up.
"Let's just thank God things turned out OK," Howat said.
Biswanger said she had not decided whether to sue SEPTA. She said she would wait to see whether she had any lasting injuries.
Contact staff writer Paul Nussbaum at 215-854-4587 or firstname.lastname@example.org.