This bridge is not located on a mainline and receives only local traffic on occasion, hence it being swung open a majority of the time.
Reportedly, this bridge has been abandoned. As the Missouri River is a navigable stream, I would suspect that the bridge could be in danger of removal.
However, there is talk of building a rail-trail from St. Joseph, MO to Wathena, KS. Perhaps they might find a way to re-use portions of this bridge if the railroad did not want to recycle the bridge. Link: http://www.sunflowertrails.org/20091229.html
Only the swing span of the bridge is over the channel. Because of the low clearance of this span, it is hard to figure out a way that the bridge could carry pedestrians without interfering with barge traffic on the river. Of the three Pennsylvania trusses, two cross dry land on the Kansas side of the river and would be out of the way of barges.
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.