Just after it left the Menlo Park Caltrain station, SamTrans bus No. 119 crashed through the crossing arm at Oak Grove Avenue around 9:20 a.m., spokeswoman Christine Dunn said.
None of the people on board -- five passengers and the driver -- were injured in the accident, Dunn said.
As the crossing arm was being repaired, trains were moving slowly through the crossing, but no service was disrupted, Dunn said.
The driver, who has worked for SamTrans for roughly 10 and a half years, has been placed on leave as the incident is investigated, she said.
The cause of the accident is not yet known, Dunn said.
Dunn said the investigation could take up to a couple of months.
Anyone who witnessed the accident is asked to call SamTrans Superintendent Karambir Cheema at (650) 508-6401.