A King County Metro bus driver drove onto the Interstate 5 express lanes in the wrong direction with an articulated bus full of passengers Wednesday afternoon.

Fortunately, nobody was hurt.

The Route 41 driver hesitated on the onramp near the Northgate Transit Center for a few seconds after passing a clearly marked “Do Not Enter” sign, then continued southbound onto the expressway, said passenger Thad White, who was sitting near the front of the bus at the time.

The state Department of Transportation tweeted Wednesday afternoon that it had “confirmed that the signage and all that was correct.”

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The lanes had just changed over from southbound to northbound, so the bus didn’t meet any oncoming traffic until it reached the Northeast 45th Street overpass, White and Metro spokesman Jeff Switzer said.

“Then you could see this wall of cars,” White said.

At that point, the bus pulled over onto the shoulder, where the driver called his supervisor, White said.

A Washington state incident-response truck diverted traffic until State Patrol troopers and the supervisor showed up, White said. The driver, who wore a “20-year safe driver” badge, told White he expected to face suspension, a drug test and mandatory retraining, in addition to a ticket.

State Patrol troopers shut down the express lanes, and the bus — then driven by the supervisor — attempted a giant U-turn to exit at the Northeast 42nd Street offramp. But the bus couldn’t make it all the way around, so a State Patrol escort led it further south to the Mercer Street offramp, where it exited the freeway, and a trooper wrote the driver a ticket, Switzer and White said.

The bus then took its passengers to Jackson Street, where it let them off.

Switzer called the incident a “very, very serious safety infraction” and said he was glad no one was injured.

King County Metro is investigating, he said.

The ordeal over, White caught another bus to the Convention Center, where he was working at an optometry convention. He had already texted his girlfriend and called his boss to tell him he’d be late.

“It was a complete scene out of ‘Austin Powers’ — but with a bus,” White said.

Colin Campbell: 206-464-2033 or ccampbell@seattletimes.com.

On Twitter: @cmcampbell6