The Maurice J. Tobin Memorial Bridge (formerly the Mystic River Bridge) is a cantilever truss bridge that spans more than two miles (3 km) from Boston to Chelsea over the Mystic River in Massachusetts. The bridge is the largest in New England. It is operated by the Massachusetts Department of Transportation and carries U.S. Route 1. It was built between 1948 and 1950 and opened to traffic on February 2, 1950, replacing the former Chelsea Bridge. The -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. Description The bridge is a three-span cantilevered truss bridge at 1,525 ft (465 m) in total length. The center span is longest at 800 ft (244 m) and the maximum truss height is 115 ft (35 m). There are 36 approach spans to the North and 32 to the South. The roadway is seven lanes wide between the shortest (439 ft; 134 m) span and the center to accommodate the now-unused toll plaza. The Northbound toll plaza was closed in the 1980s; the Southbound toll plaza was closed on July 21, 2014. History Chelsea Bridge Early transport between Boston and Winnisimmet (later Chelsea) was by the Winnisimmet Ferry. In 1803, the Salem Turnpike was extended across the Mystic River to Charlestown, where the Charles River Bridge then connected to downtown Boston. The new Mystic River bridge (Chelsea Bridge) had two draw spans and cost $53,000 () to construct. The Boston and Chelsea Railroad opened a single horsecar track over the bridge on November 20, 1858. The toll was dropped on November 9, 1869, when the bridge and turnpike became state property. The Boston portion of the bridge was rebuilt in 1877, with a new iron draw span, while the Chelsea portion was also repaired. The Lynn and Boston Railroad (successor to the Boston and Chelsea Railroad) ran a pair of horsecar tracks across the bridge. In 1880, Chelsea paid Boston $25,000 () to permanently maintain the portion of the bridge within Chelsea, including the north draw. The Boston portion was damaged by a fire on September 7, 1887. Electric streetcars replaced the horsecars on the bridge in the early 1890s, with all-electric service effective March 13, 1893. Charlestown viaduct The Boston and Lowell Railroad (B&L) purchased the Mystic River Railroad, an unbuilt paper railroad, in 1871.