WMATA said "It is alleged, and we are investigating."
Stay tuned for details if/when they become available.
3:19 UPDATE ArlNow.com has more details here.
4:21 UPDATE From WMATA:
At 1:21 p.m., a Metrobus that was not in service, struck the rear of an auto at Glebe Road and Fairfax Drive, in Arlington, VA. Three people were in the auto which was stopped at the time. The three occupants of the auto declined medical attention. There was moderate damage to the auto and the bus. The bus operator was cited.
The driver of the bus was removed from service and is undergoing the standard drug and alcohol test.
The operator has been a Metro employee since September 2000.