After skirting the northern edge of downtown, it meets the Route 8 freeway at exit 44 and briefly overlaps with US 202 just east of the interchange.

The road turns southeast and returns to more of a rural character, meeting the southern end of Route 183 before entering Harwinton, where it turns easterly at the junction with the eastern end of Route 118.

From here to its eastern end, it becomes a suburban primary arterial road known as Farmington Avenue.

The road then meets SR 508, a short freeway that provides access to I-84 while Route 4 eastbound traffic continues through one of the state's few jughandles.

After passing the University of Connecticut Health Center, it enters the town of West Hartford.

The section of modern Route 4 between Sharon and Cornwall Bridge was the Sharon and Cornwall Turnpike; from Cornwall Hollow to Torrington, it was part of the Goshen and Sharon Turnpike (which used West Cornwall Road and Route 128 between Sharon and Cornwall Hollow); the portion between Harwinton to Burlington was the eastern half of the Litchfield and Harwinton Turnpike (the western half is Route 118); and the portion from Farmington to West Hartford was part of the Farmington and Bristol Turnpike (which used George Washington Turnpike and Red Oak Hill Road between Burlington center and Route 10).

The road from Collinsville to Farmington center was designated as State Highway 138 at the same time.