A southbound train struck the vehicle at a track crossing at Angus Avenue at about 2:30 p.m., Caltrain spokeswoman Christine Dunn said. No injuries were reported, she said.
Emergency crews have responded and are working to clear the tracks.
As of 3:45 p.m., trains were running up to 50 minutes behind schedule and were expected to have to single-track around the collision site for another two hours, according to Caltrain.
Passengers on the disabled southbound train were transferred onto another train at the San Bruno station.