MARTA has launched an investigation after a man said he captured surprising video on his cellphone.

The driver said he clocked a MARTA Mobility bus speeding on Interstate 285 in DeKalb County.

The speed limit along I-285 is 55 miles per hour. Keri Robinson said he's seen it happen before, so this time he decided to get proof.

"I'm always amazed by when I see people in a position where others put their trust in them, and they abuse that trust. I don't know who was in the back of that Mobility van, whether there was someone to say, 'Hey, you're going too fast,' ” Robinson said.

Robinson said the bus was going about 75 in a 55 mph area.

He felt it was a safety hazard to everyone on the road Thursday, and admits he was speeding, trying to keep up.

"If you saw at the end, the last thing I said was I'm pulling over and slowing down now. We were uncomfortable. That was pretty fast for me, and the traffic around us, nobody was going that fast," Robinson said.

RAW: MARTA Bus Caught Speeding

Channel 2’s George Howell spoke to a MARTA spokesperson about the video, and got a statement, saying, "MARTA takes any complaint we receive very seriously. We immediately opened an internal investigation into this report. Based on the findings of this investigation, we will take appropriate action."

"If something happened, it's not just the driver who would get hurt, there's people there who can't fend for themselves. You see it on the news all the time. There's a bus, there's a van full of people, and it's going to take them out and other people," Robinson said.

Robinson hopes his video clip will remind drivers who may be speeding that they're not alone on the roads-- people are watching.

The video was shot Thursday morning.

As soon as we brought it to MARTA's attention, they were quick to get back to Howell with the statement and assurance that they will look into this.