Route 12 was replaced by Connecticut Route 32 from New London to Norwich, Connecticut Route 12 north of Norwich, Massachusetts Route 12, New Hampshire Route 12, and Vermont Route 12 from the Connecticut River to Montpelier. North of Montpelier, Route 12 was replaced with Vermont Route 14 to Hardwick, Vermont Route 16 to Barton, and U.S. Route 5 to Newport. Route 12A is now Vermont Route 12A, and Route 12B was succeeded by Vermont Route 14. Route 12 was further functionally replaced in various sections by Connecticut's Interstate 395, Interstate 190 and Interstate 290 in Massachusetts, and Interstate 91 and Interstate 89 in Vermont.
