CRANBERRY TWP — A Seven Fields man was killed early this morning when his speeding sport utility vehicle slammed into the back of a tractor-trailer on the Pennsylvania Turnpike, authorities said.

The 37-year-old man, who was not wearing a seat belt, likely died on impact about 1:30 a.m., said Butler County Deputy Coroner Larry Barr.

The man, whose name was not immediately released pending notification of his family, died of massive head and chest injuries.

State police said he was driving a 2006 Kia Sorento east on the turnpike at a high speed in the right lane when he hit the rear of the eastbound rig, about a mile and a half from the Cranberry exit.

One witness, a motorist passed by the Kia, estimated the SUV was traveling about 100 mph, authorities said.

The vehicle hit the back of the 2006 Freightliner truck hauling a flatbed trailer loaded with steel.

“I happened to look back just before I was hit and I didn’t see anything,” said Mark A. Schlesselman, 38, of Lima, Ohio, who was driving the truck. “So he must have been going really fast.”

He was not hurt.

Barr said he did not suspect alcohol was a factor in the crash.

A portion of the turnpike was closed for several hours before reopening to all traffic about 5:45 a.m.