SEATTLE — The State Route 99 tunnel has reopened in both directions after a power outage closed it completely for hours Thursday morning.

The closure caused traffic backups on city streets all around downtown Seattle, where drivers were being diverted.

WSDOT says the closure lasted nearly three hours after the equipment that switches the tunnel to its backup power feed failed.

In an email to KING 5, a spokesperson said the “switch gear that transfers the tunnel to its backup feed failed. Generators turned on, but they are not designed to run the ventilation and some of the other systems.”

Seattle City Light said the outage began when downed wires fell across the intersection at 4th Avenue South and South Hanford Street. Crews isolated the damaged section of the grid and restored power

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