Bathed in the glow of computer screens and a wall full of video monitors, Rock Hoffman grimaced as he watched a car slam into planks that had spilled onto the eastbound Schuylkill Expressway near Vare Avenue.

"Ooooh. We've got lumber in the left lane," he said. Some vehicles swerved around the wood; others slowed suddenly but couldn't avoid it.

Hoffman, 20 miles away, was almost as involved in the afternoon rush-hour traffic mess as if he'd been on the road.

He called for a Pennsylvania Department of Transportation truck to clear the lumber, and he typed a message on his keyboard that instantly appeared on a digital sign near University Avenue to warn drivers: "Debris Just Ahead in the Left Lane. Caution."

Along with colleagues Mike Crowley and Tom Collins, Hoffman was manning the nerve center for the region's highway network. At PennDot's Transportation Management Center in King of Prussia, the three were trying with varying degrees of success to keep crowded roads from grinding to a halt.

They toggled among 306 closed-circuit TV cameras to see a tour bus broken down on northbound I-95 near Vine Street, a two-car accident on U.S. 202 near Boot Road, and a disabled car in the right lane of southbound I-95 near Disston Street.

They tapped out messages, like telegraphers of old, and could watch their terse notes appear immediately in orange digital displays on some of the area's 121 roadside signs.

They notified police dispatchers, alerted traffic reporting services, called for distinctive lime-green PennDot tow trucks.

Pretty typical for a springtime afternoon rush. Controlled chaos on the roads, mellow intensity in the control room.

"We're trying to keep the lanes open," said Lou Belmonte, district traffic engineer. "Sometimes things come so fast and furious, you just have to prioritize. . . . Other days, it's like, why do you even need a TMC?"

The day the French-fry truck caught fire was definitely one of the former.

It was about 4:30 p.m. on the Friday before Memorial Day last year, on southbound I-476 near St. Davids, with the road clogged with Shore traffic.

The French-fry truck overturned and burst into flames. The resulting traffic jam took nearly six hours to clear.

"When a truck overturns like that, you get the word out as fast as you can, but there's not going to be anything but gridlock," Belmonte said. PennDot has begun installing movable median barriers to make it easier to get traffic out of such jams.

24/7 operation

The center, on the fourth floor of PennDot's regional headquarters, opened in 1993 with 12 cameras and four variable message signs on I-95. Since 2005, the TMC has been a 24/7 operation, with ever-increasing responsibilities and technological resources.

Automatic time-and-distance signs are a relatively new addition, now in place on I-95, I-476, the Schuylkill Expressway, and other major highways. The signs are monitored in the control center, but their information is automatically generated by "tag readers" on metal arms that stretch over highway lanes.

The readers register how long it takes cars equipped with E-ZPass transponders to travel between readers. That info, updated every five minutes, tells motorists how long it has just taken a vehicle to travel from, say, the Vine Street Expressway to U.S. 1 on the Schuylkill Expressway.

But the information is a snapshot of the past, sort of like the light from a star millions of light-years away. There's no guarantee that the time on the board reflects reality right now.

No recording

"By the time you get there, conditions could have changed," said Manny Anastasiadis, assistant district traffic engineer for traffic operations.

Although the traffic monitors in King of Prussia can see you on the road, they're not watching you like Big Brother, Belmonte said.

The cameras transmit real-time pictures, but they don't record. So they are of no use in accident investigations or other police matters. And the picture resolution is not good enough in most cases to read license-plate numbers or identify people.

The traffic center costs about $2.5 million a year to operate.

The 10 lime-green trucks dispatched by the traffic monitors help motorists free of charge by changing tires, jump-starting batteries, providing a gallon of gas, or refilling radiators. If they can't get you going in 10 minutes, they'll tow your car to a service area and give you a cellphone to call for help.

Last year, the service trucks made 11,513 assists.