MONROE — A woman from Eastern Washington suffered critical injuries Tuesday morning after the third serious accident on U.S. 2 in Snohomish County in less than a week.

The latest crash was reported around 9 a.m. Tuesday and occurred after an eastbound Honda Accord drove into the trailer of a dump truck that was merging from Fern Bluff Road onto the highway, according to the Washington State Patrol.

The trailer was fully loaded with sand or gravel, trooper Keith Leary said.

The cause of the accident remains under investigation.

“We aren’t going to make a conclusion yet,” Leary said. “We just don’t know.”

Both directions of U.S. 2 near Fern Bluff Road were closed for more than two hours.

The injured woman, 56, was a passenger in the car. She was transported to Harborview Medical Center in Seattle where she was listed in critical condition Tuesday afternoon.

The driver, 22, and another passenger, 19, were taken by ambulance to Valley General Hospital in Monroe. They had non life-threatening injuries.

All three were listed by the State Patrol as living in Malott, a small unincorporated community in Okanogan County in Eastern Washington.

Troopers said the truck was southbound on Fern Bluff Road and was making a left turn onto eastbound U.S. 2. The Kenworth dump truck and trailer were driven by a Monroe man, 37.

The Honda was unable to stop in time and struck the trailer in an eastbound lane, a State Patrol memo said.

Last week, there were two fatal accidents on U.S. 2 in Snohomish County.

Wayne McKenzie, 65, of Wenatchee, died near Index after a three-car crash on Friday. He was driving a van on a curvy stretch near Eagle Falls Creek when he crossed the center line, according to the State Patrol. He was taken by ambulance to the Gold Bar Fire Station, where a helicopter was waiting to fly him to Harborview. He died at the fire station.

On Thursday, a man driving a stolen car died and a man and his son were injured in a head-on collision on U.S. 2 near Snohomish west of 88th Street SE.

Statewide, there have been 57 fewer fatalities on Washington’s roads and highways in 2012 compared with the same period a year ago. There were 327 through Sept. 10 last year compared to 270 in 2011.

Eric Stevick: 425-339-3446, stevick@heraldnet.com