Route 198 was commissioned in 1932, running along the current route of Route 171 from former Route 15 (now I-84) in Union to former Route 91 (now Route 171) in Woodstock.
SR 504 was once planned to be a short freeway to connect with the Berlin Turnpike (U.S. Route 5 and Route 15) near the South Meadows Expressway connector.
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In 1963, however, the state proposed the corridor as the Cedar Ridge Connector with no number, leading from its current terminus at I-84 to U.S. 5/Route 15 in Wethersfield.
After crossing under I-84, Route 131 meets the former northern end of Route 15, which was a continuation of Connecticut Route 15.
The Wilbur Cross Highway (Connecticut Route 15) formerly ended in Sturbridge; locals sometimes call Haynes Street and portions of Mashapaug Road "Old Route 15".
Connecticut | Hartford, Connecticut | New Haven, Connecticut | University of Connecticut | U.S. Route 66 | Greenwich, Connecticut | U.S. Route 1 | Bridgeport, Connecticut | Stamford, Connecticut | Norwalk, Connecticut | New London, Connecticut | U.S. Route 6 | U.S. Route 101 | Connecticut River | Route 66 | U.S. Route 30 | New Jersey Route 4 | Mystic, Connecticut | European route E65 | U.S. Route 40 | Norwich, Connecticut | California State Route 1 | U.S. Route 1 in Maine | Pennsylvania Route 309 | Middletown, Connecticut | European route E18 | U.S. Route 23 | European route E4 | Wethersfield, Connecticut | Waterbury, Connecticut |
A small segment of Interstate 691 is located in the town of Cheshire, and connects Interstate 84 to Interstate 91 and Connecticut Route 15.