PORT TREVORTON, Pa. (AP) _ In another deadly clash between modern technology and a simpler way of life, a tractor-trailer plowed into a horse-drawn wagon carrying seven children from an Amish family, killing three of them.

The truck driver tried to stop when he spotted the black wagon Wednesday night, but his rig jackknifed when he hit the brakes. It was at least the ninth accident in recent years involving Amish buggies and motor vehicles.

``It was devastating,'' state Trooper Fred Dyroff said. ``I've been to a lot of accidents and this one really bothered me. He hit the buggy and people went flying.''

Mary Martin, 14, and her sisters Erma, 12, Vera, 7, were killed.

Their sisters, Julie, 16, and Norma, 5, were in serious condition, and 19-year-old Edith, who drove the wagon, was in satisfactory condition. Their brother, Leon, 9, was discharged from the hospital Thursday.

Truck driver Terry Chism, 32, of New Albany, Miss., suffered only minor injuries. No charges were brought against him.

The crash happened when the Martins' wagon pulled off a dirt road onto a stretch of U.S. 11 and 15, apparently returning home from a popular fishing spot in this rural region of central Pennsylvania.

Nearby, the highway changes from a winding, two-lane road to a four-lane highway, and drivers unfamiliar with the area tend to speed up.

Dyroff said he was unable to determine if the wagon pulled into the truck's path or its horse, also killed, was spooked.

The state requires lights on all horse-drawn buggies and wagons after dark. Dyroff did not know whether the wagon complied with the law, but said it often makes little difference. ``From a distance you can't see them as you approach them,'' he said.

Local drivers watch out for the buggies and wagons, but the horse-drawn vehicles catch truckers and out-of-state drivers unaware.

The Amish, a plain-living religious sect, scorn many modern conveniences as ``worldly'' distractions. Their brethren in Michigan, Minnesota and Wisconsin have won court challenges of state laws requiring their vehicles to carry the triangular orange ``slow-moving vehicle'' sign.

Mary Yoder, manager of the Dutch Kitchen Restaurant near the accident site, said Amish migrating from nearby Lancaster County drive their buggies in the middle of the road.

``Some have the attitude that the horse and buggy was here first, so it's their right of way,'' said Yoder, who was raised Amish. ``They shouldn't be allowed on the highway like regular traffic, and it won't stop with these three who died.''

At least two other motor vehicle-buggy collisions have happened in Pennsylvania. In October, a truck driver who did not see a buggy slammed into it, killing an 80-year-old Amish woman and injuring four in Mercer. In the town of Gap, a drunken driver plowed into a buggy carrying a family in 1988, paralyzing the father.

Other accidents happened in Wisconsin, Ohio and Michigan. After a semi-trailer truck struck Mary Lambright's buggy in Peru, Wis., killing her, her husband refused to accept an insurance company's $212,000 settlement. Mahlon Lambright, who was injured in the 1995 accident, said his 11 children might not appreciate Amish values when they grow up.