BART was recovering from major systemwide delays Thursday evening due to a person on the tracks in the Transbay Tube.
The person was found and arrested inside the tube about 8:15 p.m., and BART officials said it would take some time to get trains back to normal speeds and on schedule.
The person's gender and age were not available.
Trains were delayed about 20 minutes in both directions through the tube as BART police searched for the person, according to the agency. The person entered the tube just after 6:30 p.m. through the Embarcadero Station, BART officials said.
Trains continued moving through the tube during the search but at a "very slow" speed, agency officials said.
BART was not certain how the person got into the tube.