BUFFALO TWP — A delivery driver for FedEx Express was injured Tuesday morning when he tried to jump into his runaway tractor-trailer that rolled away on him at Buffalo Plaza.

The driverless rig traveled out of control through the typically busy intersection — crossing both lanes of Route 356 — before smashing into an unoccupied car parked in the driveway of a home at about 10:30 a.m.

The truck tractor pushed the car into a large tree, stopping the momentum and avoiding what could have been a worse and even freakier accident.

“If not for that car and the huge maple tree, the truck would have run into the house,” said Buffalo Township police Lt. Tim Derringer.

“And if the truck had veered a little to the left,” he said, “it would have gone down an embankment and onto Bear Creek Road.”

Police, emergency crews, onlookers and the homeowner, Gerald Watts, heaved a collective sigh of relief after assessing what could have been and learning that the FedEx driver suffered only apparent minor injuries to his back and legs.

The middle-age man, whose name was not immediately available, was treated at Butler Memorial Hospital.

Authorities believe the man was at the shopping plaza and out of his rig when the truck began rolling. The trailer contained unspecified cargo.

Derringer did not know if the man had not properly set the brakes or if a mechanical problem caused the vehicle to slip out of gear.

The delivery man saw the rolling rig and tried to jump in the door to stop it.

“He fell trying to get into the truck,” Derringer said. The man’s visible injuries were scrapes and cuts, leaving him a spectator to the unfolding freak accident.

“The truck drifted down the grade and crossed the north and southbound lanes,” the officer said. “I don’t know how it didn’t hit a passing car.”

It eventually T-boned the driver’s side of a 2000 Chevrolet Cavalier that was parked at Watts’ house in the 500 block of South Pike Road, also known as Route 356.

Had it not been for the accidental backstops, the tractor-trailer would have taken out the porch and plowed through the front of the house, the 61-year-old Watts acknowledged.

A sales representative who works in Springdale, he was not at home. He had just left a nearby bank and was driving back to his house of 36 years. He lives there with his two sons.

Son Alexander Watts was in the house. He had planned that morning to take the car to work at the Starbucks coffee shop at the Pittsburgh Mills mall.

Those plans changed dramatically.

The Chevy was bulldozed into the tree. Derringer was already close by at the township building when he heard the crash.

“It was almost bent around the tree,” Watts said of his now totaled car.

His tree didn’t fare much better.

“A huge piece of bark was ripped off it,” Watts said, “and large branches were knocked off, too.”

But Watts’ immediate concern was not for his property but for the delivery man.

“I gave him a chair from the porch to sit on,” Watts said. “He was in a lot of pain.”

And like first responders, passers-by and bystanders, he couldn’t fight feeling fortunate.

“It’s a miracle that truck made it across (Route) 356,” Watts said, “without hitting anyone.”

Said Derringer: “A lot of things worked out in our favor.”