support a fourth lane in each travel direction for future expansion. The $365-million (equivalent to $ in ), widening project was completed in 2005 from Burlington to the New Hampshire border. The final section of the expressway was planned for inner suburban towns northwest of Boston, Massachusetts. The expressway was to supply a new route for US 3, between Route 128 and the canceled I-695 (Inner Belt). This was one of the expressway projects canceled in Governor Francis Sargent's 1970 moratorium on expressway construction within Route 128. The latter section of the expressway was a key component of the "Master Plan Highway Plan for Metropolitan Boston". The highway would have traveled through Lexington, Arlington, Medford, Somerville, and Cambridge, before linking with the Inner Belt Expressway. The original plan called for US 3 and Route 2 to link up at the Lexington–Arlington border and continue southeasterly, crossing Route 16/Mystic Valley Parkway at the Arlington–Somerville border and proceeding into Cambridge toward Union Square, Somerville. A 1962 plan called for Route 2 and US 3 to converge at Alewife Brook Parkway with a longer stretch of new highway for US 3 paralleling Lowell Street in Lexington and Summer Street in Arlington. Exit numbers along the Northwest Expressway section in Massachusetts were to be changed to mileage based numbers under a project to start in 2016, but that project was postponed. However, in November 2019, the MassDOT announced it would be proceeding with the project in late mid-2020. Terminuses According to the American Association of State Highway and Transportation Officials (AASHTO) route log, the southern terminus of US 3 is at the junction of Route 2A and Route 3 in Cambridge, which is where Route 2A crosses the Charles along the Harvard Bridge (also known as the Massachusetts Avenue Bridge). This is a change from AASHTO's 1989 Route Log which placed the terminus at US 20 in Boston, where Route 2 currently meets US 20 after crossing the Charles River at the Boston University Bridge. This was where US 3 met US 1 until that highway was rerouted in 1971. The original northern terminus of US 3 (in 1926) was at Colebrook, New Hampshire, but the highway was extended to West Stewartstown in 1928 and to Pittsburg in 1937. Colebrook was the northern terminus again from 1939 to 1940. Since 1940, the highway has run through Pittsburg to the Pittsburg–Chartierville Border Crossing. Major intersections