The bus struck the rear of another vehicle around 1 p.m., causing that vehicle to crash into two other cars, said Trooper Chris Webb with the Washington State Patrol.
Nine people on the bus and two others in other vehicles were taken to local hospitals. A Harborview Medical Center spokeswoman says the nine patients that went there were all in satisfactory condition. Webb said the bus driver and those in the first vehicle hit suffered from broken bones.
The crash blocked all eastbound lanes of the freeway for about 90 minutes before getting one lane open around 2:35 p.m. and being completely cleared a short time later.
During the closure, WSDOT officials worked to get cars trapped on the bridge behind the wreck to turn around and head back to I-5. The backup on I-5 from the closed bridge extended several miles in each direction during the height of the closure, officials said.