Route 40 begins at an interchange with I-91 in North Haven as a continuation of Bailey Road.

The road soon enters the town of Hamden, where it crosses over the Mill River and closely parallels Route 22 for the rest of its alignment.

[1] Plans for the Mount Carmel Connector first appeared in Tri-State Transportation Commission's recommendations of 1962.

[2] Originally the Mount Carmel Connector was to be part of the freeway relocation of Route 10 to exit 29 of I-84 in Southington.

[3] The Mount Carmel Connector was opened in 1972 from I-91 to Dixwell Avenue and State Street (US 5) in North Haven.