US 4 highlighted in red
|Length||252.62 mi (406.55 km)|
|South end||US 9 / US 20 in East Greenbush, NY|
|East end||I-95 / Blue Star Turnpike / US 1 Byp. / NH 16 in Portsmouth, NH|
|States||New York, Vermont, New Hampshire|
In the state of New York, US 4 begins at the concurrency of US 9 and US 20 in East Greenbush. Heading northward, it has an interchange with I-90, continuing northward into Troy. In Troy, it passes by Hudson Valley Community College as well as the headquarters of the 42nd Infantry Division. US 4 then heads downhill, passing the historic South End Tavern as Burden Avenue, named for the historic Burden Iron Works. Later, US 4 assumes Fourth Street, which splits into parallel one-way streets (Third Street handles southbound traffic). Once through Troy's historic downtown, the streets meet and pass by the Green Island Bridge, later passing under the Collar City Bridge and into Lansingburgh.
After Lansingburgh, US 4 turns left to cross the Hudson River on the Troy-Waterford Bridge, entering Waterford, joining with NY 32 to head north together west of the Hudson. After Mechanicville, US 4 and NY 32 split, and US 4 passes by the Battle of Saratoga and the Saratoga National Cemetery. NY 32 joins again to pass through Schuylerville, after which US 4 splits off to cross the Hudson one last time.
In the state of Vermont, US 4 immediately becomes a four-lane divided expressway. The historic routing of US 4 runs nearby as VT 4A, which later becomes Business US 4 as it enters Rutland. South of Rutland, US 4 meets US 7 and overlaps it into downtown, meeting the east end of its business route. East of Rutland, US 4 is a two-lane highway, meandering through the Green Mountains, passing by Killington, going through Woodstock and Quechee, crossing the Quechee Gorge, and meeting US 5, I-89, and I-91 at White River Junction. Crossing the Connecticut River, US 4 enters New Hampshire.
In the state of New Hampshire, US 4 passes through Lebanon, meeting I-89 again. It then heads southeast to Boscawen, where it briefly overlaps US 3 before joining I-93 into Concord. Turning east, US 4 briefly overlaps I-393 and for a longer stretch with US 202. Passing through Durham, US 4 joins the Spaulding Turnpike at Dover Point and travels southeast to its eastern terminus in Portsmouth at the Portsmouth Traffic Circle.
Prior to being designated US 4, the road from Whitehall, New York eastward through Vermont was New England Interstate Route 13 (NE-13). From the Vermont-New Hampshire state line to Franklin, New Hampshire, it was the eastern extension of NE-14. From Franklin to Concord, New Hampshire it used NE-6 (now US 3), and from Concord to Northwood, New Hampshire it used NE-9 (now NH-9). Between Northwood and Dover, New Hampshire, it used a road that was previously not numbered. From Dover to its eastern terminus at Portsmouth, New Hampshire, the road used to be known as NE-16 (now NH-16).
1926-1930: Glens Falls, New York at the point where US 9 split into US 9W and 9E, to Portsmouth, New Hampshire.
1930–: East Greenbush, New York, following former US 9E, through its former west terminus, to Portsmouth, New Hampshire.