Route 40 is the remaining vestige of various plans for a New Haven bypass, dating to the early 1940s. The bypass would have connected a proposed Route 10 freeway in Hamden to Interstate 95 in Branford.
The first bypass: Route 22
When the Wilbur Cross Parkway (Route 15) was fully open in 1949, there was still no easy way around New Haven to shore points east. Early plans for the area expressway network showed a proposed eastward spur from Route 15 to East Haven; however, that was never built.
To help guide traffic around northern outskirts of New Haven, a new numbered route was created incorporating old Route 168 and Route 141, as well as most of Route 139. This new route -- Route 22 -- was created in 1951, and today zigzags along the modern Route 40 corridor.
Plans for a freeway bypass
Statewide freeway plans in the 1960s included a new highway around New Haven, connecting Route 10 in Hamden to I-95 in Branford. The Tri-State Transportation Council plans called this the Route 22 Expressway. In 1968, when the federal government asked states to nominate additions to the interstate highway system, Connecticut's position was that the the system should not be expanded; however, if it was, the state would nominate a twelve-mile loop around New Haven. This was not granted.
The Mount Carmel Connector
In the early 1960s, the state planned three New Haven-area connectors from I-91 to US 5 and Route 10. These were:
The Mount Carmel Connector would extend north and west from Interstate 91 at Bailey Street in North Haven to Route 10 near Ives Street in Hamden.
By 1964, planners had arrived at a location and treatment for the Connector close to what was eventually built. A semi-directional three-level "T" interchange would be built at I-91, with ramps from the Connector to Bailey Street; this was built as planned. A nonstandard interchange involving a divided Dixwell Avenue at State Street was not built as planned; instead, a more conventional set of hook ramps were built at Dixwell Avenue and Devine Street.
A partial interchange was planned at the Wilbur Cross Parkway. There is no interchange at all today: the only place in Connecticut where two freeways cross with no access between them. The original plan would have provided three ramps:
- 40 NB to 15 NB
- 40 NB to 15 SB
- 15 SB to 40 NB
A full trumpet interchange was planned at the Connector's terminus at Route 10. The inner loop ramp to Route 10 southbound was omitted, and traffic instead makes a left turn at a traffic signal.
Route 40 opens in sections
The first part of the Connector, from I-91 to Dixwell Avenue, opened in 1972. The state's numbering, SR 724, was not signposted. The remaining 1.8-mile section to existing Route 10, in the design stages, was referred to as the Relocation of Route 10.
In 1976, the remainder opened, extending SR 724 to Route 10. The state had been referring to the new freeway as the Route 10 connector up until the time it opened. Signs for Exit 10 on I-91 once labeled the highway as "To Route 10".
The other Route 40
In 1970, the state was planning to apply Route 40 to a project on Boulevard (now Ella T. Grasso Boulevard) in New Haven: a four-lane bridge, with approaches, over what is now the Metro North railway. The project length was 0.5 miles, while the distance from I-95 to US 1 (the probable extent of a Route 40 designation) was 1.2 miles.
The bridge was completed in 1978, two years after the Route 40 designation had been given to the Mount Carmel Connector, and the Boulevard itself became part of Route 10.