The crash, which involved a car and two trucks, happened just after 6:30 p.m. Thursday, according to police.
A white box truck and a purple Ford pickup collided in the middle of the bridge. Medics transported one of the drivers to Harborview Medical Center with "life threatening injures," according to the Seattle Fire Department.
No one else was injured in the crash.
With the bridge impassable, traffic on Aurora Avenue ground to a halt as the Seattle police investigated the accident.
The bridge reopened at about 12:30 a.m. Friday.