BOSTON -- The Massachusetts Bay Transportation Authority's new zero tolerance policy on workers carrying cell phones is being put to the test, with yet another driver under investigation after cameras caught him allegedly talking on a phone outside his bus.

NewsCenter 5's Rhondella Richardson reported that video captured by NewsCenter 5 shows the driver of MBTA bus No. 2368 stopping outside the Franklin Park Zoo just before 7 p.m. Wednesday night, talking on his cell phone outside the bus in violation of 'T' policy.

When the conversation finishes, the driver re-boards the bus. The MBTA said it would launch an investigation into the incident following NewsCenter 5's inquiries.

An MBTA Green Line trolley crash at Government Center in May allegedly involved a text-messaging driver at the helm of the trolley. Close to 50 people were injured in the collision and the MBTA issued a zero-tolerance cell phone and PDA ban for all bus, train, van and boat drivers. Just carrying a phone while on the job is punishable by a 10-day suspension and possible firing.

Talking on a cell phone is cause for automatic firing. Last week, the MBTA followed through with its first firing of a driver for talking on a cell phone. In that case, the driver allegedly borrowed a cell phone from a passenger and made an unauthorized stop to get off the bus and chat.

An MBTA spokesperson said the driver outside the Franklin Park Zoo would be interviewed on Thursday.