My understanding is that the bridge is still used, but only on rare occasions. If the bridge was abandoned completely, it would probably have to be demolished immediately as the Missouri River is a navigable stream.
Not too sure this is "open to traffic"... look at satelite and street view; the swing span seems left in the open position.
This four span bridge consists of one movable (swing) span, and three, twelve panel, pin connected, Pennsylvania through trusses.