The problem occurred on the southbound tracks between the Burlingame and San Mateo stations and caused delays of up to about 30 minutes beginning around 7 a.m. The cause has not yet been determined.
By 10:30 a.m., trains were operating on both tracks but the southbound No. 236 train was running eight minutes behind schedule and the No. 134 train was running 11 minutes late, according to Caltrain spokeswoman Christine Dunn.
The northbound No. 135 train was also running about 11 minutes late.