SEPTA has resumed running trains on the Market-Frankford line after smoke was reported in the track area.
The transit agency ran shuttle buses between 5th Street and 30th Street for about an hour while crews made emergency repairs.
SEPTA spokeswoman Heather Redfern said the smoke was reported near the 13th Street and 15th Street stations. Crews were making repairs to the third rail in that area, she said.
The smoke was seen shortly after 10:30 a.m.
It wasn't immediately known what exactly was damaged, and SEPTA is continuing to investigate.
Trolleys briefly halted stops at the 15th Street station.