U.S. Route 4 in 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 from downtown). At Congress Street, in the middle of the Central Troy Historic District with St. Paul's Episcopal Church on the corner, it intersects NY 2. Once through downtown, the streets meet and pass by the Green Island Bridge, later passing under the Collar City Bridge and onto Second Avenue in Lansingburgh.[9]

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. They run along the riverbank for 7 miles (11 km) to the city of Mechanicville, where the routes cross over the Anthony Kill and intersect NY 67 in the central business district. US 4 and NY 32 continue on, passing through the nearby village of Stillwater before splitting at Bemis Heights, a small community 5 miles (8 km) northeast of Mechanicville. While NY 32 follows a more inland routing along the western edge of Saratoga National Historical Park, US 4 continues to follow the riverbank, running along the eastern boundary of the park. Past the park, the route passes by the Saratoga National Cemetery before rejoining NY 32 at the southern edge of the village of Schuylerville.[9]

US 4 begins to run along the Champlain Canal after Schuylerville, passing through the hamlets of Northumberland and Starks Knob. At a crossing over the Hudson River, US 4 and the concurrent NY 32 split in different directions. US 4, which is now on the other side of the Hudson, continues northward through Fort Miller, and crosses the River once more. The route then enters Fort Edward, where it becomes concurrent with NY 197.[9]

US 4 northbound at 106th Street in Troy. At left is the Hudson River, which US 4 follows from Troy to Hudson Falls.

With the Hudson River to its west, US 4 heads northward once again, leaving NY 197 behind. Not far after Fort Edward, the highway enters Hudson Falls, where it turns into a local road. There, it heads through downtown, intersecting with NY 196, and soon afterwards, NY 254. US 4 makes a sudden curve to the northeast, heading through the rural regions for the rest of its length.[9]

There is one final intersection with NY 32, but they do not become concurrent and US 4 heads to the northeast. The route passes through Kingsbury and soon after, becomes concurrent with NY 149. The two routes head into Fort Ann, where they split, with NY 149 heading westward. After passing Battle Hill, NY 22 merges in from Comstock. There are several hills before the intersection where the two roads split in Whitehall. US 4 continues along its final stretch after NY 22, passing fields and such to the state line, where it continues into Vermont.[9]

In 1911, the New York State Legislature created Route 43, an unsigned legislative route extending from the southern village line of Stillwater to the western village line of Schuylerville via the hamlet of Quaker Springs.[10][11] On March 1, 1921, Route 43 was renumbered to Route 44 to eliminate numerical duplication with another legislative Route 43 in western New York. At the same time, Route 44 was extended southwest from Stillwater to Clifton Park via Mechanicville and west from Schuylerville to Saratoga Springs.[12]

The first set of posted routes in New York were assigned in 1924. Two of the routes assigned at this time were NY 6, a north–south route extending from the New York City line to the Canadian border, and NY 30, another north–south route connecting NY 6 in Mechanicville to the Vermont state line west of Fair Haven.[13] NY 6 left Albany on modern NY 32 and followed it to Mechanicville, where NY 6 veered westward on what is now NY 67 and NY 30 picked up the current alignment of NY 32. NY 30 continued north on modern NY 32 to Glens Falls, at which point it went east to Hudson Falls via Warren and River streets. It headed northward from there to Vermont on modern US 4. From Mechanicville to Schuylerville, NY 30 utilized the alignment of legislative Route 44. By 1926, NY 30 was rerouted north of Whitehall to continue north toward the Canadian border. The old alignment of NY 30 between Whitehall and Vermont was not assigned a new number. Meanwhile, an alternate route of NY 6 on the east side of the Hudson River between NY 5 (now US 20) in East Greenbush and NY 6 in Waterford was designated as NY 6B by 1926.[14]

Entering New York on US 4 southbound

In the original plans for the U.S. Highway System, the north–south highway along the western bank of the Hudson River was designated as US 9 while the highway on the eastern bank was assigned US 109. The two routes were concurrent from Albany to Mechanicville, where US 9 went west to follow NY 6 while US 109 continued north on NY 30. The designations met again south of Glens Falls, where US 109 ended at US 9. Also in the original plans was US 4, which was assigned to all of NY 30's original alignment between Glens Falls and the Vermont state line.[15] In the final system alignment approved on November 11, 1926, the routing of US 9 was altered to follow its modern alignment between Albany and Glens Falls while US 109 was reconfigured to use NY 6B between East Greenbush and Waterford.[2]

When U.S. Highways were first posted in New York in 1927, US 9 was restored to its originally planned alignment between Albany and Glens Falls (via Waterford and Mechanicville) while the US 109 designation went unassigned. The portion of US 109's alignment south of Waterford became US 9E instead. US 4 was assigned as planned in 1926, overlapping NY 30 between Glens Falls and Whitehall. The NY 6 designation was completely removed at this time.[16] In the 1930 renumbering of state highways in New York, US 9 was realigned to follow its modern routing between Albany and Round Lake. The portion of US 9's former routing between Waterford and Mechanicville as well as all of US 9E north of US 20 became a southward extension of US 4, which left its original alignment in Hudson Falls and followed a previously unnumbered riverside highway south to Northumberland. In between Northumberland and Mechanicville, it utilized the former routing of NY 30, which was reassigned to another highway as part of the renumbering.[17][18]

North end of the northern US 4 / NY 32 overlap in Northumberland

Virtually all of US 4 south of Hudson Falls initially overlapped other routes, all of which were assigned as part of the renumbering. In between Hudson Falls and Northumberland, US 4 overlapped NY 32B, which began in Glens Falls and followed US 4's former routing east to Hudson Falls. From Northumberland to Schuylerville and from Bemis Heights to Waterford, US 4 was part of NY 32. The segment from Schuylerville to Bemis Heights was designated NY 32A. Lastly, the part of US 4 south of Northern Drive (then-NY 40) in Troy was concurrent to NY 40.[19] By 1932, NY 40 was rerouted through Troy to follow a more easterly alignment through the city. The realignment moved the northern end of the overlap southward to the junction of US 4 and Winter Street in North Greenbush.[20]

Most of the overlaps were eliminated as time went on. In the early 1940s, NY 32A was reassigned to another highway in the Catskill Mountains while NY 32B was truncated to end in Hudson Falls. The former routing of NY 32A became a realignment of NY 32, creating an uninterrupted overlap between US 4 and NY 32 from Waterford to Northumberland.[21][22] In the mid-1950s, work began on a project to upgrade a pre-existing riverside highway between Bemis Heights and Schuylerville.[23][24] The project was completed by 1958, at which time the roadway became part of a realigned US 4.[25] The overlap with NY 40 was eliminated in the late 1950s when NY 40 was truncated to begin at the junction of US 4 and Winter Street.[25][26]