Speed may have been a factor in the crash, said Sgt. Dan Shades of the Washington State Patrol.
Shades said the crash happened at about 6:15 a.m. in the westbound lanes of the highway near Ehli Hill.
The driver of the Chevy pickup truck was eastbound and somehow crossed the concrete jersey barrier and was hit head-on by a Ford Focus in the westbound lanes, he said.
A large articulated dump truck hauling a full load of gravel in the westbound lanes then crashed into the car and pickup.
The drivers of the pickup and car died at the scene. Their names have not been released. Shades said both of the crash victims were men.
The man driving the dump truck was uninjured.
Shades said investigators have not yet determined how or why the pickup truck crossed the jersey barrier.
"We're doing a very thorough investigation to determine exactly what happened," he said.
He said it's possible the pickup may have rolled as it went over the barrier, but it was right side up when it was hit by the car and dump truck.
Speed may have been a factor in the crash, but that remains under investigation. Alcohol is not believed to be involved.
Shades said it appears the dump truck driver did not have time to stop or avoid the collision.