FORT LAUDERDALE (CBS4) – Lazaro Solano was driving his sister Margy Perez home from the airport in Fort Lauderdale Sunday night, when a seemingly bizarre episode played out in front of them on southbound Interstate 95.

A pair of state troopers zoomed up into traffic just in front of Solano and began changing lanes, slowing down, their emergency lights flashing their brightest.

“They cut everybody off. They didn’t allow anybody to pass them. They started swerving, zigzagging,” Solano told CBS4′s Gary Nelson Monday.

His sister Margy captured the event on her iPhone5 video cam. The video shows the troopers slowing traffic to a near crawl before one of the officers speeds off ahead. The second trooper begins to do figure eights across the multiple lanes of highway, driving back and forth, back and forth, from shoulder to shoulder.

On the cell video Margy Perez can be heard wondering if car thieves had stolen the squad cars and were joyriding.

“I think they…stole the state troopers’ cars,” she says. “They stole those cars.”

Margy was so alarmed by the seemingly bizarre behavior of the squad car zigzagging across the expressway that she called 911.

“Why is he doing that?” she says on the video. “That’s not normal. I know that’s not normal.”

Well, Margy, it actually is normal.

“It is a traffic-pacing or rolling roadblock maneuver,” FHP Sergeant Mark Wysocky explained to CBS4 News. “We use that procedure occasionally when we need to remove a large piece of debris from further down the roadway.”

Wysocky said troopers also execute the rolling roadblock maneuver when there is an accident up ahead or a crew working in the middle of the highway. The idea is to keep traffic from cresting a hill at 70 or 80 miles per hour and encounter an obstruction.

“It slows the traffic down like it’s supposed to, and we don’t have another car come over a bridge and into stopped traffic and cause a crash,” Wysocky said.

Lazaro Solano was relieved to learn the troopers were performing a by the book procedure, intended to keep motorists safe.

“You know, you just never know,” Solano said. “You really never know.”

Well, now you do.