They are replacing the westbound truss bridge, the old bridge was shifted over to allow for a temporary detour, allowing for a new bridge to be constructed on the exisitng westbound alignment.
In typical logical gov't thinking, the eastbound structure also requires replacement. However, the detour is scheduled to come out prior to rebuilding the eastbound bridge. I priced the project, but wasn't low bidder!
If interested, the work including shifting the bridge and rebuilding the westbound bridge is approx. $11m