The Connecticut Department of Transportation (CTDOT) maintains a system of state highways to serve the predominant flow of traffic between towns within Connecticut, and to towns in surrounding states. State highways also include roads that provide access to federal and state facilities (Special Service Roads).
The state highway system consists of roads indicated on the official CTDOT map and highway log. As of January 1, 2007, the state highway system contains a total of of roads (not including ramps and interchange connections), corresponding to approximately 20% of all roads in the state. All state highways are state-maintained except for several segments (totaling 4 miles) that are locally maintained. Interstate highways and U.S. highways in the state are not Connecticut state routes, however they are maintained by the state.
All state highways are given a number designation. All state highways are assigned Route numbers. Route numbers are in the 2–999 range. State highways that are special service roads are assigned SSR numbers and are unsigned; these numbers are above 399 and are used for internal CTDOT purposes. Signposted state highways that are not U.S. highways or interstates are signed with the square Connecticut state highway shield.
State routes
Routes are signed state highways and are assigned numbers from 1 to 399 (with the exception of I-684 and I-691). All state, U.S. and Interstate highways are part of the same numbering system. In 1926, the U.S. highway system was implemented. U.S. Routes 1, 5, 6, and 7 were used as designations on several primary state highways, replacing New England routes 1, 2, 3, and 4, respectively. The other New England routes that were not re-designated as U.S. routes became ordinary state highways but kept their number designation, which are used even today (with some realignment). In 1958, Connecticut received approval for the route numbers of its three primary Interstate highways: I-84, I-91, and I-95. State highways with the same number designation as the Interstate highways were renumbered to avoid duplication of route numbers.