U.S. Route 1 (US 1) is a part of the U.S. Highway System that extends from Key West, Florida, to the Canada–United States border at Fort Kent, Maine.

In many of the latter communities, it begins to intermittently follow the route of the historic Boston Post Road and often still carries that name.

It remains a busy urban and suburban artery all the way to Connecticut, often four lanes wide and serving as the main street of many of the communities it passes through once it leaves the city.

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.

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.

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.

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.

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.

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.

It crossed into the mainland on Kingsbridge, then continued through a largely abandoned road to Williamsbridge, then across the northern part of the Bronx along Bussing Avenue.

In 1800, the Westchester Turnpike company was chartered to build and maintain a toll road between New York City and Connecticut.

The old Westchester Turnpike alignment was designated as NY 1, which matched the route number across the Connecticut state line.