The accident happened around 7:30 a.m. when southbound train No. 312 collided with the tractor-trailer near the Broadway station in Burlingame.
The truck had failed to clear the intersection, and when the train entered the crossing it clipped the truck's rear, Dunn said.
The warning bells, signals and gates at the intersection were operating properly at the time of the collision, according to Dunn. The truck driver sustained minor injuries. No one on the train was hurt, she said.
The accident initially stopped service in both directions, but Caltrain reported around 8 a.m. that trains were being allowed to pass through the area on a single track. Both tracks reopened around 8:50 a.m.
Several trains were delayed until about 10 a.m. and the incident prompted the cancellation of northbound train No. 231 and southbound train No. 218.
An investigation into the official cause of the collision is under way.