The video shows the officer driving in reverse in traffic, and it's been viewed about 14,000 times.
"I hope he knows he shouldn't be breaking the law," said Christine Pham, who witnessed the incident. "If I can't reverse in traffic, neither should he."
Pham watched from her office window as the officer made the same maneuver over and over Wednesday afternoon.
"I would say seven to nine times," said Pham.
While hard to see from her cell phone video, she watched the black and white squad car, with its police lights on, drive in reverse down the Central Expressway service road into oncoming traffic.
Drivers took notice and slowed to pass the officer.
"My colleagues were like, 'What is he doing? That has to be illegal,'" said Pham. "Yeah, he is a cop, but why is he reversing like that?"
Pham posted the video on Dallas Police Department's Facebook page.
DPD responded by asking for details and told FOX 4 that the incident has been turned over to a traffic supervisor.
The department says officers are discouraged from ever creating a hazard during traffic enforcement.
Officer-turned-lawyer Pete Schulte thinks the incident will become an example.
"I think what's going to happen is they're going to use this as a training tool and say, ‘Look, you're always being watched,'" said Schulte. "It may be legal, but is this good public policy to be doing this where the public is seeing this sort of activity?"
Pham says she often sees cops stop speeders on the service road, but she says most finish writing tickets, then drive around the block to return to the same spot.