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.
Special Service Roads
Roads classified by the Department of Transportation as special service roads are given an unsigned number designation between 400 and 499. Special service roads are roads that connect a federal or state facility (including state parks and some Interstate Highway interchanges) to a signed state route. These numbers only appear in internal documentation, none of them are signed.
State Roads
State Roads are state-maintained roads that are usually long entrance/exit ramps to/from an expressway, or short interconnecting roads between signed routes. Roads classified by the Department of Transportation as state roads are given an unsigned number designation between 500 and 999. The first digit denotes which Maintenance District the road is mainly located in: 500–599: District 1: Greater Hartford 600–699: District 2: Quiet Corner, Lower Connecticut River Valley, Southeastern Connecticut 700–799: District 3: Southwestern Connecticut, Greater New Haven 800–899: District 4: Naugatuck River Valley, Greater Danbury, Northwestern Connecticut 900–999: Statewide; very short routes
State road numbers are only for internal record-keeping and documentation, all of these roads are unsigned.