Thanks Nathan, seems obvious now that you told me but I couldn't figure it out for the life of me.
Wayne, they are indeed an alteration to the structure. To increase vertical clearance, part of the sway bracing was removed from the bridge. Those braces were added to the outside of the superstructure to make up for the loss in lateral stability.
Wonder what those extensions are for on the portals and along the upper chord ? Looks like a later edition but I can't imagine for what. Anyone have any ideas ?
This bridge is gone. It was replaced earlier this year, 2013-14, and the road was realigned. Part of the old road is now extra parking for the Iron Bridge Inn restaurant.