A train operator pulling into the station at about 8:50 a.m. noticed someone on the tracks and immediately hit the "stop" button, BART spokesman Linton Johnson said.
The train, which was traveling at about 35 mph, took several seconds to stop, he said. Seven train cars rolled over the woman, who apparently survived by lying between the rails, Johnson said.
BART police responded within 10 minutes and found the woman, who is in her 40s, covered in soot and sitting near the top of the stairs with her head in her hands, Johnson said. It's unclear how she climbed out from under the train.
She suffered cuts and bruises and was taken to San Francisco General Hospital, he said. BART does not release conditions of patients.
Johnson said it is not surprising that the woman survived, and that people who fall onto the tracks and can't get out are advised to lie flat between the running rails or get underneath the lip of the platform, then stay still and yell for help.
"If the train comes it's most likely you will survive because of the depth of the trackway between running rails," he said. "There's quite a bit of room."
The trains also do not pass at all under the platform lip, he said.
The Glen Park station was closed for nearly an hour after the incident, with only some trains able to pass through. The station was cleared at about 9:45 a.m. but there were still residual delays, BART said.
The train operator is being put on standard paid administrative leave during the investigation and was given a drug test Thursday morning, Johnson said. The operator will also be offered psychiatric help.
During the closure, most southbound BART trains were turned around at the 24th Street/Mission or Montgomery BART stations in San Francisco, Johnson said.
Trains bound for San Francisco International Airport single-tracked through the Glen Park station and were delayed by about 15 minutes, according to Johnson.
Other passengers experienced major delays heading into San Francisco from the East Bay.