A woman was struck by southbound train No. 210 on the tracks at Charleston Road at 7:35 a.m., Caltrain spokeswoman Christine Dunn said.
Dunn said there were 322 passengers on the train at the time, and no one on board was injured.
Trains were initially stopped in both directions and a bus bridge was set up. Dunn said at about 8:20 a.m. that trains had begun single-tracking through the area on the northbound tracks.
About two hours later, the southbound tracks reopened and trains were moving through Palo Alto at reduced speeds. However, service was still behind schedule and Dunn said it would take "some time" to get back to normal.
As of 10:45 a.m., some trains had been canceled and delays of up to 97 minutes were reported.