Night photography image of the Boston Tobin Bridge photographed in early spring at twilight. The Maurice J. Tobin Memorial Bridge (also referred to as the Mystic River Bridge) is a cantilever truss bridge that spans more than two miles from Charlestown to Chelsea over the Mystic River in Massachusetts. The bridge is the largest in New England and is operated by the Massachusetts Department of Transportation. It was erected between 1948 and 1950 and opened to traffic on February 2, 1950, replacing the former Chelsea Street Bridge. The 36-foot wide roadway has three lanes of traffic on each of the two levels with Northbound traffic on the lower level and Southbound traffic on the upper level.