RALEIGH, N.C. — North Carolina Highway Patrol troopers have increased their presence on major highways across the state in a campaign to crack down on speeding.

Operation Slowdown started Monday with the state Highway Patrol boosting its staff and using helicopters to catch speeding motorists along the state's major four-lane highways, including Interstates 40 and 95, in 23 counties.

"We have instructed our troops to aggressively crack down on speeders," said Col. W. Fletcher Clay, with the Highway Patrol. "Our troopers will still enforce all traffic laws, but we will concentrate on speeders."

During the first Operation Slowdown last year, the patrol's increased staff resulted in more than 16,000 tickets being issued, mostly for speeding, which resulted in a 17 percent drop in speed-related collisions.

But that success was overshadowed by the nearly 1,200 people, including 174 teenagers, who were killed on the state's highways in 2005.

The Highway Patrol decided to start the operation after conducting a study in 2004 and discovering just how fast people driving on highways. When it looked at its citations between 1999 and 2004, it discovered a 150 percent increase in tickets for people going over 100 mph, with triple-digit speeds in excess of 140 mph becoming more common.

Patrol officials say switching around schedules in order to increase the staff, as well as using extra patrol cars and helicopters, is an expensive effort that can only be done for a limited time.