The highway then crosses the Connecticut River by way of the Charter Oak Bridge, curving to a more east-west direction, before merging into the median of I-84 in East Hartford.

In 1968, the I-84 designation was moved to a proposed highway from Hartford to Providence, and the then-cosigned portion with Route 15 was renumbered to I-86.

[3] The Route 15 designation remained cosigned with I-86 section south of the Massachusetts border until October 1, 1980, when it was truncated to its current northern terminus at exit 57 of I-84.

[3] On June 9, 2015, Governor Dannel Malloy announced a five-year, $200 million construction project to rebuild the interchange between US-5/CT-15 and I-91 at the west end of the bridge.

Although the interchange was rebuilt during the late 1980s and early 1990s along with the Charter Oak Bridge and the US-5/CT-15 portions of the Wilbur Cross Highway, traffic along the section has increased significantly since the reconstruction and the removal of the two connector ramps between I-91 and the Founders Bridge (CT-2), which is located further north, closer to Downtown Hartford.

The Charter Oak Bridge took over these connections following its replacement in 1991, and became the main southeast bypass of Hartford for traffic traveling on I-91 and I-84.

These upgrades will improve connections between I-91 and I-84[4] The Charter Oak Bridge itself is not being replaced as part of the I-91/US-5/CT-15 interchange project.