Twenty-two-year-old Dustin Diamond, of Mona, died Saturday morning after police believe he fell asleep behind the wheel, said Utah Highway Patrol Sgt. Ted Tingey.

Diamond was going south on I-15 about 5 a.m. when his Ford SuperCab pickup crossed into the median of the highway and hit a roadway post, Tingey said. The driver then swerved right, hitting rocks lining the right shoulder of the freeway, where the vehicle rolled.

Diamond was ejected from the vehicle and died on scene, near mile post 238, about 15 miles north of Nephi.

Also on Saturday, three other people were involved in a rollover accident that killed Layton resident Amber Ward, 22, Tingey said.

Ward was driving a silver Ford Taurus north on I-15 at a high rate of speed when she hit a concrete barrier while exiting onto Riverdale Road in Weber County about 1:30 a.m., Tingey said.

The initial impact sent the car into a guardrail, and it rolled. Ward was ejected from the vehicle and died about 10 a.m. at Ogden Regional Hospital from her injuries, Tingey said.

Kathrine Yates, 22, of Syracuse, who was a passenger in the car, was treated at Ogden Regional and later released. Jared Gallegos, 25, was also in the car and was treated on scene for minor injuries, according to UHP.

Gallegos was arrested and booked into the Weber County jail on outstanding warrants, Tingey said.

Police believe alcohol and speed contributed to the accident, which shut down the offramp for about two hours, Tingey said.

ngonzalez@sltrib.com