Complex sentence: The bridge crosses diagonally over an older single-tracked railroad-only bridge carrying the Grand Junction Line, formerly owned by CSX Transportation but purchased by the Commonwealth of Massachusetts for the MBTA in 2010.
Split into simpler sentences: The bridge crosses diagonally over an older, now single-tracked railroad-only bridge carrying the Grand Junction Line. This bridge, formerly owned by CSX Transportation, was purchased by the Commonwealth of Massachusetts for the MBTA in 2010.