The biker was heading northbound just before 9:30 p.m. when he crashed near First Avenue South, according to police.
It's unclear what caused the crash, but the rider was thrown from his bike and went over the side of the viaduct, landing on Railroad Avenue.
A witness who was below the viaduct at the time of the crash said the rider's helmet flew off when he went off the road.
He was pronounced dead at the scene.
First Avenue South and the northbound lanes of the viaduct were temporarily closed to traffic while police investigated the crash.