The bus had been having mechanical issues this morning, before a mechanic was called. The driver and mechanic were working on the bus around 8:38 a.m. when the bus got lose and drifted down the street, finally being stopped by a at O'Farrell Street.
"There are strict policies in place to prevent this type of thing from happening, and it appears none of these policies were followed," Muni spokesperson Paul Rose said.
The Muni operator and mechanic will be tested for alcohol and drugs and have been placed on administrative leave. The operator has been placed on nondriving status, Rose said.
The front of the bus was damaged in the crash, which blocked northbound traffic on Van Ness for more than an hour this morning.