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UPDATED at noon with information from press conference.

ST. LOUIS • Police don't plan to let a huge gathering of motorcycle stunt riders here this weekend get out of hand like a similar one did last year.

The Streetfighterz Ride of the Century 2012 is being promoted as a Saturday event in St. Louis on social networking sites such as Facebook, where more than 2,000 people had indicated as of Thursday that they would or might take part. Related events are set to start today, according to Internet postings, and by early evening there were already large groups of motorcycles on area interstates.

St. Louis County Police Chief Tim Fitch said that police didn't have advance notice of last year's ride, when thousands of motorcyclists frightened drivers on local interstates — with stunts that included zooming between cars and driving into oncoming traffic — and taunted police.

"We were caught off guard last year," Fitch said. "Now we've had an opportunity to prepare. We will be ready for them."

Fitch said two motorcyclists were killed in last year's rally and one lost a leg. Law enforcement was inundated with calls about the riders' dangerous stunts.

"It was pretty intense last year at our 911 center — we probably received several hundred 911 calls when they were in town, and that doesn't include the calls other agencies got," Fitch said.

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St. Louis County police won't be alone in the effort to keep the riders in check.

The Missouri Highway Patrol, St. Louis Police Department, St. Charles County Sheriff's Department, St. Charles Police Department, Illinois State Police and the Missouri Department of Transportation are joining the enforcement effort. They discussed their preparations for the invasion of motorcyclists at a news conference this morning.

"There's going to be hundreds of them out. They'll be all over the place," Highway Patrol spokesman Trooper Juston Wheetley said Friday. "We're just going to be vigilant in our enforcement efforts. We're just going to do the best we can."

In addition to calling in dozens of extra officers for reinforcement, Fitch said the agencies plan to monitor the bikers from the sky. "You can't outrun a helicopter," he said.

He also said St. Louis County officers will take a hard line against riders who cause problems. Last year, disruptive riders were ticketed. This year, he said, they will be taken to jail.

And, Fitch said Friday, police will collect insurance information from motorcyclists who are pulled over, then send a letter to the insurance company specifying why the cyclist was stopped.

Fitch said most of motorcyclists are young people, so he urged parents who know their children own "street bikes" to stay home this weekend and leave their bikes in the garage.

"Because when they get out in these crowds, peer pressure takes over and they're liable to some things they wouldn't normally do," he said.

There's no way to know in advance how many riders will be here for the event, which is for riders of sport bikes specially designed for speed and stunts. The gathering is being billed as the 10th and final ride of its kind on its Facebook event page. Many riders indicated on that site that they have already signed in at local hotels.

Organizers could not be reached for comment.

Fitch advised motorists on the region's "main drags" to call authorities if they see packs of hundreds of riders.

Motorists who see illegal activity should call *55 to the reach the Highway Patrol or 911 to reach the closest police agency.

The gathering of motorcyclists in St. Louis comes on a weekend with several big events, including the Great Balloon Race in Forest Park.

"We're going to have a lot of people on the highways, and the last thing we need are stunt drivers," Fitch said.

Fitch said the motorcyclists are welcome, as long as they behave.

"What we hope is they will come to St. Louis and enjoy the city, but what we won't tolerate is them driving on our highways and endangering their lives and other people's lives," Fitch said.

Joel Currier of the Post-Dispatch contributed to this report.

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