Route 3 is a 14.48-mile (23.30 km) long route connecting Middletown to the Glastonbury-East Hartford town line. It passes through the towns of Cromwell, Rocky Hill, Wethersfield, and Glastonbury. The northernmost 3 miles (4.8 km) of Route 3 is an expressway that was originally intended for the cancelled Interstate 491.

Route 3 begins at Route 66 in Middletown. It is a secondary, minor arterial road from Middletown up to its interchange with Interstate 91 in Wethersfield. It crosses, but does not have a direct interchange with the Route 9 freeway in Cromwell (access is via Route 372) and with Interstate 91 in Rocky Hill. The last 3.5 miles (5.6 km) of Route 3 from the Interstate 91 interchange in Wethersfield to East Hartford is freeway. Then Route 3 freeway crosses the Connecticut River on the William H. Putnam Memorial Bridge from Wethersfield into Glastonbury. The freeway has one intermediate exit into Glastonbury. Route 3 ends at an interchange with the Route 2 freeway just after crossing into East Hartford. The last 0.75 miles (1.21 km) of Route 3 is the merging ramp from Route 3 northbound to Route 2 westbound.

Route 3 through the town of Rocky Hill is also known as the Disabled American Veterans Memorial Highway.

Route 3 was established in 1941. It originally ran from West Street/Berlin Road in Cromwell, which was part of Route 72 at the time (now Route 372), to the Silas Deane Highway (Route 99) in Wethersfield.

In late 1958, as part of the planned Interstate 491 (a southeastern bypass of Hartford), a freeway from I-91 to Route 2, crossing the Connecticut River on the Putnam Memorial Bridge, was opened. The Route 3 designation was temporarily extended along this freeway pending completion of I-491. In 1973, I-491 was cancelled due to local opposition and the Route 3 designation along this freeway segment became permanent.

In 1991, when the Route 9 freeway through Berlin and New Britain was completed, Route 72 was truncated to end at Route 9 in New Britain. The east–west portion of the old alignment of Route 72 was reassigned to an extended Route 372 (running along Berlin Road/West Street to end at Route 99 in Cromwell). The north–south portion of old Route 72 from Cromwell to Middletown (ending at Route 66) was reassigned to Route 3.