A Medford woman died in a multiple-vehicle accident Thursday on the Long Island Expressway after sideswiping a tractor trailer and being hit head-on by another car, Suffolk County police and sheriffs said.

Yong Soon Yim, 76, was going west between exits 61 and 62 in Holtsville when the accident happened about 1:10 p.m., authorities said.

"Witnesses said she was entering the roadway from the shoulder . . . and came into the path of the tractor trailer," said Michael Sharkey, chief of staff at the Suffolk Sheriffs Department, which responded to the accident.

When Yim hit the tractor trailer, which was in the right lane, she lost control, careening from the right lane to the left lane, authorities said.

"Her car was spun around, so it was facing east, and a westbound SUV hit it head on," Sharkey said.

Yim was taken to Stony Brook University Medical Center, where she was pronounced dead, police said.

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The driver of the Mercedes-Benz SUV, Richard Regan, 55, of Valley Stream, and his passenger were treated for nonlife-threatening injuries at the same hospital.

The tractor trailer driver, Kevin Blake, 33, of Massachusetts, was not injured, police said.

The westbound lanes were closed for about four hours as Suffolk police investigated the accident. The lanes reopened shortly after 5:30 p.m.

The Mercedes and Yim's Hyundai were impounded for safety checks. The tractor trailer was examined at the scene.

Sixth Precinct detectives ask anyone with information to call 631-854-8652 or anonymously to Crime Stoppers at 800-220-TIPS.