Washington State Patrol officials say Michael A. Robertson, 25, was driving his SUV west in the eastbound lanes of the freeway when he slammed head-on into the woman's Mazda near the Montlake exit at about 5:25 a.m. on April 4.
The victim, Morgan F. Williams, 58, of Seattle, was a 32-year employee of Eddie Bauer, and her ex-husband says she was on her way to work when the crash happened.
Robertson earlier had pleaded not guilty to the vehicular homicide charge at a May 9 court hearing at which he broke down in tears. But weeks later he decided to change his plea to guilty, and formally did so Friday in King County Superior Court.
Robertson wiped away tears as the judge read from Robertson's signed confession: "I was impaired with the alcohol I consumed when I drove the wrong way on 520."
Investigators say Robertson was driving home after drinking with his friends in Seattle. He originally entered the freeway heading east toward Bellevue but apparently made a U-turn on the freeway and accelerated back toward Seattle, prosecutors said.
After the collision, firefighters had to cut the roof off of Williams' Mazda to rescue her after she was trapped in the mangled wreck. She was taken to Harborview Medical Center in critical condition, and later died of her injuries. Investigators say they found an empty bottle of whiskey in Robertson's front seat.
Friday, Williams' family and friends gathered for support in the courtroom.
"We are very pleased that (Robertson) has taken responsibility," said Jan Fick, Williams' sister-in-law. "And we think he has done the right thing is doing that."
Fick remembered Williams as an exceptional woman.
"We all just have a hole in our hearts that she's gone," Fick said.
Prosecutors said Robertson likely will be ordered to spend the next 10 1/2 years prison during his sentencing on July 26.
Robertson's attorney said her client will accept the sentence.
"He doesn't seem particularity concerned about the penalty he faces," said Ramona Brandes. "He's always said, 'I'll take whatever penalty I'll have, it can't make up -- I took this woman's life.' "
Robertson's sentence will also include a guilty plea to a DUI committed in Pierce County in December 2012.