At 325 miles (523 km), U.S. Route 9's (US 9) New York segment accounts for more than half the highway's total length. It runs from the New Jersey state line in the middle of the George Washington Bridge to a cul-de-sac just south of the Canadian border north of Champlain. It is the longest north–south U.S. highway in the state.

The highway's passage through the state offers a diverse sample of New York to a traveler, taking in busy urban neighborhoods, suburban strips and forested wilderness. It is Broadway in Upper Manhattan and the Bronx. It uses parts of the old Albany Post Road in the Hudson Valley, where it passes the historic homes of a U.S. President and Gilded Age heir. It passes the center of New York political power in downtown Albany, and the patrician grandeur of Saratoga Springs. It penetrates into the deep recesses of the Adirondack Park and runs along the shore of Lake Champlain.

US 9 spawns more letter-suffixed state highways than any other route in New York, including the longest, 143-mile (230 km) NY 9N. Outside of the cities it passes through, it is a mostly a two-lane road, save for two expressway segments in the mid-Hudson region. For much of its southern half it follows the Hudson River closely; in the north it tracks Interstate 87, the Adirondack Northway.

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