Oregon State Police said the crash happened around 1:30 Thursday afternoon near milepost 33.
According to OSP, a man driving a motorcycle rear-ended a semi-truck on southbound I-5. Police believe speed was a factor. The motorcyclist was taken to the hospital with serious injuries, the driver of the semi-truck was uninjured.
Police did not release the identity of the motorcyclist involved.
Both southbound lanes of I-5 were closed and traffic was diverted to the shoulder of the road. Both lanes re-opened around 3:00 p.m.
OSP said the investigation is ongoing.