Complex sentence: Fall 2011 will mark the closure of the existing bridge, in which construction of the replacement piers, approaches and superstructure is scheduled to last a full year, with the opening in the fall of 2012.
Split into simpler sentences: Fall 2011 will mark the closure of the existing bridge, in which the construction of the replacement piers, approaches and superstructure will begin. The second phase is scheduled to last a full year, with the opening of the new bridge set for the fall of 2012.