U.S. Route 1 in New York

US 1 enters Manhattan on the George Washington Bridge together with I-95 and US 9. The concurrency between US 1 and US 9 that began at Woodbridge 31 miles (50 km) to the south ends at the first exit, when US 9 splits to the north to follow Broadway. The expressway continues another mile (1.6 km), crossing under several buildings in short tunnels before crossing the Harlem River via the Alexander Hamilton Bridge into the Bronx. It is bookended by an exit to the Harlem River Drive on the west and the Major Deegan Expressway (I-87) on the east.[2]

The Alexander Hamilton Bridge

The busy highway, now known as the Cross Bronx Expressway, continues another two miles (3.2 km) until US 1 leaves it at Webster Avenue, one of the Bronx's longest streets, in the Tremont section of the borough, on a northerly heading. A mile and a half (2.4 km) beyond the Cross Bronx, US 1 turns right (east) onto Fordham Road, near the eponymous university. At this busy transportation hub, the road also crosses Metro-North Railroad at Fordham station. Due to the prohibition of left turns from Fordham Road to Webster Avenue, southbound traffic on US 1 requires taking a detour onto Washington Avenue and East 189th Street.

Erroneous "Interstate US1" shield at the intersection between US 1 and Gun Hill Road. This sign has since been removed.

US 1's eastward heading trends to the south as it enters Bronx Park a mile (1.6 km) to the east, after a complex junction with Southern Boulevard. In the park, it crosses the Bronx River, where it trends back to the north again, and has a full cloverleaf interchange with the Bronx River Parkway. Immediately following that, it turns north on Boston Road, the first section of the Boston Post Road it follows into Connecticut. This slants northeast across the eastern outskirts of Williamsbridge past Gun Hill Road into Eastchester, where it starts to veer eastward again, to a route more closely parallel with I-95. At Provost Avenue, NY 22, New York's longest north–south route, starts a journey to the Canada–United States border. After leaving Provost Avenue, US 1 then crosses the Eastchester Bridge named for the neighborhood it passes through. The bridge passes over the Hutchinson River and then descends toward Ropes Avenue to the south, where it leaves New York City.

One-quarter mile (0.40 km) into the village of Pelham Manor, the Hutchinson River Parkway crosses over, with access available in both directions. Now Boston Post Road, it crosses the village and, another mile (1.6 km) to the northeast, has another interchange at I-95 (now the New England Thruway) just after entering New Rochelle at Pelham Country Club. Just after that it crosses under Amtrak's Northeast Corridor.

A mile (1.6 km) past that junction, in New Rochelle's busy downtown, US 1 divides, with northbound traffic staying on Main Street while Huguenot Street takes southbound drivers. The roads rejoin after another mile, at Pratt Street, as the surrounding neighborhood becomes more residential. New Rochelle gives way to Larchmont after another mile (1.6 km) and returns to being Boston Post Road. A mile and a half (2.4 km) later, after passing through downtown, NY 125, a short route to White Plains, leaves to the north at Weaver Street. The junction with NY 125 is just north of the Larchmont village limits.

After another few blocks, US 1 comes to the Mamaroneck town line. Here, it comes closer to Long Island Sound when it passes Harbor Island Park a mile (1.6 km) from the municipal boundary, and then enters the village at Mamaroneck Avenue. A mile (1.6 km) past that junction and downtown, NY 127, also bound for White Plains, forks left at Keeler Avenue as US 1 itself begins to trend more to the east into Rye, passing Rye Neck High School at the town line.

Whitby Castle, part of the Boston Post Road Historic District in Rye

To the right of the wooded area to the north is the Boston Post Road Historic District, a National Historic Landmark (NHL) characterized by mansions and homes that have remained unchanged since before the Civil War including the Jay Estate, Lounsberry, and Whitby Castle. The road begins to head more to the north after passing it and Rye Golf Club, to its intersection with Playland Parkway, which leads to the popular amusement park, Rye's other NHL.

One mile (1.6 km) past this junction, US 1 crosses downtown Rye, where NY 120 forks off to the north at Purchase Street, and then passes through the junction that marks the eastern terminus of I-287, the Cross-Westchester Expressway, crossing it and I-95 again in the process, with access to both. Immediately afterward it enters Port Chester, its last community in New York.

It curves a bit toward the east here, crossing the railroad tracks again after an industrial area, then turning left on South Main Street to follow a more northern route through the working-class city's busy downtown, where NY 120A touches at Westchester and King streets to eventually follow the New York–Connecticut border back to its parent route.

Now North Main Street, US 1 continues through downtown Port Chester to cross under the tracks again. Traffic lessens here as the neighborhood grows less commercial, and, a half-mile (0.80 km) later, at Putnam Avenue, the road crosses the Byram River into Greenwich, Connecticut, at the beginning of a brief split (southbound traffic enters New York on Hillside Avenue).