The driver was going south on SR-509 just before 1 p.m. when he lost control on the overpass to I-705, struck the curb and vaulted over the barrier, said Trooper Guy Gill with the Washington State Patrol.
The car then plummeted 32 feet down onto the northbound lanes of I-705 below, killing the driver, Gill said. There are no reports of any other injuries.
The driver's name has not been released.
Gill says tire marks leading to the edge of the overpass indicate there was no attempt by the driver to brake or steer before the car hurdled over the edge.
All northbound lanes of I-705 were blocked for the investigation but reopened later in the afternoon.