In the 1920s, state highway 313 followed today's Route 30 between US 5 and Route 83.
Much of today's Route 313, which was commissioned in 1963, has been state-maintained since the 1930s.
River Street in Seymour was part of Route 8, from 1936 until the Route 8 freeway opened on Jan. 3, 1962. Then River Street became unsigned SR 728.
Broad Street was also part of Route 8 until 1936, when Route 8 was moved to River Street and Broad Street became part of Route 8A. In 1962, Broad Street became unsigned SR 713, the basis for Route 313's eventual number.
Rimmon Road and a small part of Maple Street were SR 563, which was designated in 1936. Some maps show this erroneously as SR 561.
In 1960, the state Committee to Reclassify All Public Roads recommended including SR 563 as a continuous state route extending to Route 8 in Seymour. In 1963, SR 563, SR 713, and part of SR 728 were combined into a new designation: Route 313.
Route 313 freeway once planned
In the 1960s, the South Central Connecticut Planning Region proposed a freeway along Route 313, from the vicinity of a Route 10 freeway in New Haven to Route 8 in Seymour. Route 313, along with Route 34 and Route 17, would have served as a radial commuter route into New Haven.
Route 313 extension planned in 2003
In 2003, a Seymour construction company proposed extending Route 313 two miles northward, from Route 67 in Seymour to Route 42 in Beacon Falls. If extended, the road would run between Rimmon St. and Rimmon Hill Rd. to the west and Route 8 to the east. This would open up 230 acres -- one of the largest tracts left in town -- for light industrial use.
In March 2003, representatives of the construction company met with the Valley Council of Governments (COG), the local planning agency, to work toward getting approval from ConnDOT: they are interested in extending the route designation, not just the road.
In April 2003 the COG approved the conceptual plan: this didn't mean construction could start, but made it easier to apply for funds. In late 2003, the Valley COG identified the Route 313 extension as a candidate for future High Priority Project funding under the federal TEA-21 program. The project cost was listed as $3.5 million.
In April 2007, the COG solicited engineering firms to further study the Route 313 extension, otherwise known as the Route 42 & 67 Connector Road. The project has been quiet since then.